Reply to your questions.
I dont own an iphone, although I wish I had another great toy, but...... I've played with many for countless hours. I've possibly played with my brothers Iphone more than he has. Anyways, here's what I think
1) My favorite thing about the iphone is eye candy/ consumer friendly OS. There is not one phone that comes close to this. I am currently a windows mobile user but I am pretty jealous of how easy things are on the phone. The iphone's eye candy just makes you want to keep playing with it more and more. Even just the little transitions from one interface to another just flips me out.
2) The least favorite thing about the iphone is the lack of MMS. You can send pictures through your email provider through the iphone but I am so perplexed why they didn't include this feature in such a great phone. Even though most people use MMS messages for silly stuff, it's just nice to have. Alot of my friends constantly send me pictures all the time, or even other type of media messages. Don't get me wrong, the iphone has so many benefits that people I could live without the MMS if I was an everyday user.
3) Favorite third party app is Palringo. Palringo takes advantage with the 3G easily. Through this you can keep in touch with other users, have a group chat, send pictures to other users. You can use your Palringo account, along with AIM, Yahoo Messenger, Windows Live Messenger, ICQ, and even Goggle Talk! How awesome is that. You can take picture with your phone and send it to whoever in real time. Several of my friends and co-workers all talk on there. Some of them do not have unlimited text messages, so they just meet on there. What would have been my favorite app was the tethering program that was released just for a week or so and was pulled off of Itunes. Too bad it's not on Itunes now since ATT is going to come out with a $30 a month tethering application on top of your $30 internet access. Just another way to make more $$$$. You might want to look into how to copy applications from other peoples iphones, especially if they have that program.
4) Tap Tap. Oh my GOD!! This game is awesome if you are into the genre of music beat games. It's in the same realm of Guitar Hero, Rockband, Frequency, Amplitude, and Dance Dance Revolution. Best of all, it's free! You can even download more songs for free! Also it displays how great the graphics and horse power the processor has on the iphone! I've spent more than 6 hours in one day playing that addicting game! Dang it!
5) I feel ya on the jailbreak! It would be so tempting if I had an iphone. Here's my opinion on it. First I would not jail break the phone, just because of the warranty but if it was covered by a 3rd party insurance company I would. Your phone is a huge investment, and it would be a shame if something went wrong with your iphone. On the other hand, if a 3rd party insurance company covered your iphone completely, I'd jailbreak it, and if it gets broken, oh well, get another one!
This is just my opinion on the iphone 3G!