I've got a 3GHz Intel Core Duo, 4gb ram, 1gb on the vid card, and 32 bit XP. After about 30 min to an hour LR2.1 locks up on me (just the program, not the computer), but all it requires is a restart, and everything is good for another hour or so. I only lose my very last input.
I upgraded to LR2.2 and it was worse. The lockup occurred about as often, but upon restart I had lost all input since I started the session. I immediately went back to 2.1.
I'm having no problems with Bridge, CS4, or Camera Raw.
I've read several posts claiming that some people are able to "unlock" the program merely by minimizing and restoring. This doesn't work for me.
I used to use ACR only, and couldn't see much advantage for me to use LR, but now I would have a hard time giving up the LR adjustment brush and graduated filter. Sure I can do it on CS4, but having everything I need to process about 95% of my photos on one screen and doing it all in one step sure speeds up my workflow.