Well I got my S2 on an 18 month contract from Phones4U... But it was an upgrade so might be different to a brand new tariff (can't see how though)
As for being slow and annoying - nope - it's seriously quick and can't see how it could be annoying, everything is pretty much customisable so you can just change things around, I've truly been converted to Android! Just to back up the speed - I was streaming a high def movie wirelessly to my tv and texting at the same time with no bother whatsoever, no stuttering, stalling, slowing down at all.
I've hammered the phone today and still have 50% battery at the moment so I'm happy with the battery life - but that's with GPS, WiFi, live wallpapers, loads of widgets, movie streaming, etc etc