A lot of the time it doesn't even start up. I just see the logo that you get when it's starting up, and it won't go beyond that. Then, after trying a lot of times it will start up, but by now it takes just a few clicks to make it crash. It used to be better, but it takes 2 minutes at most now for the program to freeze.
Also, my PokerStars screenname misses a few hundred hands in the 'Player Summary' section compared to the Player Statistics section. The Player Statistics section is correct, so apparently the hands were imported somewhere, but they do not show up in most of the stats. This is even without any filters on. (The crashing happened before the missing hands, but it's been worse since.)
I'm running on Vista.