I just did this a month ago. Loved my BB but I'm also an Apple freak. It is very different, but a really great kind of different. I use my phone for business and pleasure. Apple somehow managed to make my job just a little more fun as far as I'm concerned, yet maintain my business needs as well. The only thing you don't have with the Iphone is a lighted notification of your emails when they arrive to your phone. I am one that constantly checks my phone anyway, so it really wasn't that hard to get over. My phone is everything to me. My mp3 player, sometimes my camera, my alarm in the mornings, my appt minder. You name it, I use it for everything it's got going on. Apple however has added some really cool things to their phone that I am really enjoying on top of the normal things. And the screen. Can't say enough about it. It's so much easier to read, surf the net (which is very fast btw) and the photos it takes are awesome.
I have the 32gb because as I have always been taught, get the larger one because you never know what you will end up having to keep on it. This way you will be prepared. I have over 2000 songs, not so many photos yet, about 10 games and 4 business apps loaded so far and I've only used 6 gb. Yes it's $100 more, but I've no regrets.
As far as transition....Apple makes their products for ease of use. To me it's a ton easier to use than a BB. I was tired of hunting for the icon I needed on a BB to get to where I needed to go. Every icon u need for each program is right there in front of you. Email is a few more steps, but again, I can deal with that.
Best thing for you to do is to go to a Verizon store and use the display. Don't let anybody bother you and take as long as you want. I did this 3 different times in a week before I bought mine. I was worried about the transition from pecking on keys to the virtual keyboard. I was amazed how quickly I learned to use that part of it. I love this part of it now.
I loved my BB's, and I kind of felt like a traitor LOL, but the Iphone is butter smooth and I'm all Apple now and not looking back.
As far as the Iphone 5, who knows. So many rumors and nobody really knows the release date of that phone. In my opinion, they won't release until spring 2012. I only say this because of much collected data I have read and that really makes the most sense for Apple and Verizon due to when they released the IP4 this past Feb.
If you do decide to get it, you have 14 days to love it or hate it. You loose $35 in restocking fee if you decide to return it, but you will then know that you tried it and not question it later.