I also have a 2G. I bought a 3GS a few weeks ago and returned it after a week.
The 3G speeds are nice, as are things like the compass and GPS but I realised I really didn't need them. Or barely used them. And annoyingly enough when I did have one of those "I'll use my iPhone to look it up!" moments I never had 3G

(when I did have 3G though it often seemed faster or equal to my home wifi)
The camera's ok as well, but still nothing compared to the 3.2MP camera phone I had back in 2007. Video recording is really quite nice for a phone. Not choppy at all, but cycorder also does perfectly passable videos for me in good light and bearable ones in low light.
As for the speed increase, it is there but I probably wouldn't have noticed it unless I'd looked for it. It's about a second, 2 max faster on opening all my apps. (but then again, on a daily basis I don't run any huge apps)
My real problem with it was that I thought once I'd used the thing for a few days I wouldn't be able to stand using my 2G, but they felt like exactly the same phone. Oh, and the battery life felt the same as on my 2 year old 2G - fab
I'm going to wait around until they at least change it a little now - bigger better screen, different casing, new OS, much better camera and battery