Former 9000 user here...
Laggy software...I've been too lazy to do it myself yet, but everything I've heard here and elsewhere re: the .246 OS indicates that it is much improved
Keyboard...this was my biggest worry too. I found the 9000 to be the best I'd ever used and still feel that way. It takes some getting used to the smaller one on the 9800, but eventually I have (same can be said for using a touch screen). Part of it is psychological...realizing RIM will likely never again come out with a 9000-sized device...RIP.
Memory...my biggest frustration with the 9000 (along with the camera). I believe the Torch started around 350 MB free. I have a ridiculous number of apps and stuff on my Torch just because I can, and I am still over 200 MB free. As usual, the more memory on devices, the more the apps tend to bloat though. Have seen some very simple apps/games in the 3 to 4 MB range. But it is nice to be able to try things out and not have to worry about squeezing them into the Bold.