There isn't an immediate difference. When I first got mine from a S1, I admit it took me a bit to get the hang of the typing...which surprised me.
By the end of the day...anyone who's ever seen me type, no matter what phone they use...even my friends with S2 owners...make comments about how I can type incredibly fast. It's effortless now...I tried typing on my other friend's S1 not too long ago...I kept tripping up on the screen since I'd literally press the next key before the screen was able to physically depress.
Most people don't realize that the screen on the S2, in all actuality, never physically moves.
I'm not lying when I say I can type almost as fast on my S2 as I can on a keyboard. I crank out emails and BBM's like nothing.....SMS's are a different story...RIM as yet to release an OS that gets rid of the God awful lag you get while typing SMS messages.
My favorite thing about it though (since my speed on the S1 wasn't bad either) is the fact that, as of now, I have about 80-100 apps and about 5 themes...my memory never drops and I've never had to pull out the battery...and I've had the phone since launch day.
Battery life could be better since it lasts about a day...less than that if I'm on it a lot. But I just get into the habit of charging it whenever I go to bed and I'm good...if I don't, I'll wake up to a dead battery.
My next phone will certainly be a Storm3 though.....unless RIM is stupid and decides not to let it have LTE functionality.
My friend, before I got the S2 absolutely HATED my S1, even on 5.0 OS. She had her heart set on upgrading from her Pearl to a Tour...until she played around with the S2 once I got it...she got the S2 instead and couldn't be happier.