I've had my SGS2 for just a month now, and have finally mastered it. The phone is now running a custom ROM from Paradox (root) and has all the software I need to make life good. Last month I figured I'd finally switch over to T-Mobile after working here for a year and a half... Got a pair of Samsungs (Galaxy S for my wife and SGS2 for me) at Costco for total cost of $179. Of course I'll have to pay the higher rate plan but it still saves money over the full retail price in the store.
I used the Skyrocket Root kit for rooting the phone on 2.3.5 (i believe it also works on 2.3.6), and downloaded the 2.3.6 Paradox ROM from http://downloadandroidrom.com/file/GalaxyS2TMobile/roms which has HUGE battery improvements:
and WiFi calling. Note: it does NOT have the Swype keyboard, but I don't use that one anyway. Been really happy with the ROM, since it is stripped of almost all of the standard bloatware. Even had to download FB, Twitter, and MyAccount but that's no big deal. I love the slick effects and UI tweaks. Can't wait til there's a new version available.
Just make sure you install Clockwork Recovery Mod before rooting.
You can get the root kit from links at the forum http://forum.xda-developers.com/showthread.php?t=1340710
just follow the instructions, put the phone in usb debug mode and hook er up.