I have been a BlackBerry user for a long time, and I am leaving it behind for the iPhone.
The iPhone is full of potential while the BlackBerry grows more and more stale each year. The BlackBerry OS that is currently in RIM's phones (the Bold included) runs on the same basic core architecture as BlackBerry devices from 3-4 years ago. I can grab my 8703e that was released in 2006 and put it next to my Curve 8310 that was released at the end of 2007, and there will be next to no difference between the two outside of the casing and a few hardware features. Worse than that, I can compare my Curve to a coworker's 7250 from even longer ago, and the same thing applies. Sure, they have added a couple software features, like some mini-menus and video recording, but the core is what determines the OS's future, and the core of the BB OS is old and weak at this point.
The BlackBerry OS is old and is getting outdated. It presents a huge hurdle for future development, and for any sort of strong third party application support. The iPhone, on the other hand, runs a desktop class OS and has the hardware power to back it up. The iPhone OS allows for amazing third party development, and that reason right there makes the future of the OS a very bright one.
If you sign up for the optional MobileMe service and you will get push mail, push calendar, and push contacts. The only one of those things that you can get on a personal use BlackBerry is the push mail.
The built in iPhone calendar doesn't support separate calendars for different classifications (like business, personal, family, etc), but Outlook does, and if you use the MobileMe service, it will push the separated calendars to your phone in different colors, just like it shows up in your Outlook or iCal calendar.
The BlackBerry does not have a stronger calendaring application, and it is easily one of the devices weakest points. If you compare the BlackBerry calendar to the iPhone's calendar without MobileMe, they are about identical in functionality. When BlackBerry OS 4.5 finally gets released, it will finally allow categorization to the BlackBerry calendar, which is something that it has lacked on personal BB devices up until this point. The Bold should have this as well. The iPhone calendar does not support categorization without MobileMe, but it is far, far easier to look at. The one major downfall of the iPhone calendar is that it doesn't have a week view.
In short, when it comes to stock Calendars, neither of them excel. The BlackBerry has week view and will have categorization soon, the iPhone is easier to use and easier to look at. With MobileMe, the iPhone calendar becomes more functional than a personal use BlackBerry calendar due to push services. It is mostly a wash in this department.
Address book/contact management? The iPhone is just as capable as the BlackBerry. They both support contact search, they both allow for multiple phone numbers, addresses, emails, etc; for each contact. They both support categorization. Where the iPhone wins this department is with the addition of MobileMe. MobileMe will allow for push contact support, and push contacts is something you can't get on a personal use BlackBerry.
Email? Email LOOKs a million times better on the iPhone because it is full HTML. HTML email is coming to BlackBerry, but it requires server side changes on the part of your carrier, and nobody knows how well it is going to work as of yet. The iPhone dominates the BlackBerry in the area of attachment viewing as well. The BlackBerry has push email included with the data plan, so you will get your email instantly without the need to subscribe to a MobileMe type service (keep in mind that MobileMe gives you far more than just email though). On the flipside, the iPhone supports full IMAP, which the BlackBerry doesn't. This means when you delete an email on the iPhone, it also deletes on your mail server inbox, if you move an email from one folder to another on the iPhone, the change also happens on the mail server inbox. The shortest interval you can set your iPhone to check for mail without MobileMe is 15 minutes. To me, I can wait 15 minutes to have a much more viewable email experience, attachments I can actually read, and IMAP support. MobileMe, of course, negates the 15 minutes by providing push mail services.
Features? The BlackBerry has more. BlackBerrys have MMS, A2DP, and cut/paste, while the iPhone is lacking these things. All three of them can come via firmware updates however, so discounting them as future possibilities shouldn't be done. These three things also depend on how important they are to you. MMS and A2DP mean absolutely nothing to me, but I do miss cut/paste. I am hopeful that it will still come as well, so that eases the pain of not having it a little bit... How important are they to you?
I would also like to mention that there is a very real, and very easy work around to the missing MMS functionality. You can use email to receive and send MMS messages in the exact same fashion you would use the MMS client. You just need to tell the people that MMS you to send it to your email address. If they add your email address to your contact info on their phone, they simply need to choose it, instead of your phone number, when they send you an MMS as usual.
When you receive the MMS, you will also get to see your friends' phones' MMS email addresses. Add this address to their contact info, and if you want to send them an MMS, all you have to do is open the picture you want to send, choose send via email, choose their phone's MMS email address instead of their phone number, and hit send. It is the exact same number of steps as sending a normal MMS, and they will not know the difference when they receive it. The ONLY thing that changes is swapping their phone number for an email address, and them swapping yours for an email address. It is very, very simple, and it works 98% of the time. Yeah, there are times it doesn't work, but it seems to be carrier specific, and it also seems that the people that can't receive MMS in this fashion have trouble even receiving it the old fashioned way, unless it was sent from their carrier.
Hardware? The iPhone beats the BlackBerry. It is a better built device, and has stronger internals. The Bold has a 624mhz processor, 128mb of RAM, 128mb of flash storage (used to store/run the OS AND any third party applications), and 1 gig of strictly storage space (can only be used for media). The Bold does support up to 32gig micro SD cards, but the SD card can only be used for media storage as well. Third party applications can't be installed to the SD card, and nothing can be run from there. Not to mention, 32 gig cards aren't available yet, and they are bound to be stupid expensive. A Best Buy bought 8 gig card currently runs about $150...
The iPhone has a 624mhz processor as well, but it has 512mb of RAM. It, as you know, has 8 or 16 gigs of storage that is all inclusive. The 8/16 gigs stores/runs the OS, third party applications, and is used to store media. You are not limited to a measly 128mb of flash memory to house the OS AND your third party applications.
The keyboard is hit or miss. You will either like it, or you won't. If you approach it with an open mind and actually take the time to learn it, I am sure you will be fine. Even if you don't come to love it, you will become adept at using it, and the rest of the features of the iPhone should outweigh your distaste for the keyboard. Only you can decide how your experience with the keyboard pans out...
For me, the iPhone wins hands down. It has an OS that packs a massive punch and gives it absolutely amazing future potential. MobileMe gives Exchange level support to all individual users, and the user interface is second to none. IMAP support is great, and actually being able to read my attachments goes a very, very long way. To me, all of these things far, far outweigh the small list of missing "features."
You do whatever you need to, but I will take the potential and incredible user experience of the iPhone over RIM's famous push email, outdated OS, and extra couple of features any day of the week, and twice on Sunday.
I would also like to say again that I am not a 3 week BlackBerry user. Unlike most of the BlackBerry fanboys, I have actually used one for about 2 years, and I have taken the time to learn the device inside and out.