I came from a Tour and let me tell you, it's night and day. I love absolutely everything about this phone. Some previous posters are misguided about some things though:
1) the iPhone hands down has the better email system. Images load lightning fast, the email is in the form the sender wanted you to see it as, and NO TRUNCATING. it also threads you emails, which is flipping nice.
2) iPhones most certainly can send attachments in emails. I don't know where people are learning otherwise... Yes, the iPhone doesn't have a file manager, but that's because that isn't how the iPhone works. It treats everything like an app, so you just have to get an app to store the files. It's really simple, and I'll gladly help anyone with more questions on this. I've sent pics, documents, PDFs, and audio clips all in emails straight from my phone. It's definitely possible and very simple to do.
I personally prefer the iPhones calendar. I like that I can change around what calendar the event goes under, and that I can add calendars like Class, Work, and Deadlines asopposed to calendars by email. The Notifications are preferable to me as well. I check my phone habitually anyway, did with my BB too, and so I just never miss them. It's also nice that when you get the popup, if you wanna reply intakes you right to the message (no opening the inbox, etc) or you can hit cancel and no boubou light will be pestering you to read the thing.
I do miss BBM, but if the current rumor is true, we might see it soon in iOS...