I've also noticed this problem with 2005. Mostly though, I've noticed the screwed up mates. Things will be great, then 5 minutes later it's full of mate errors for no reason. Close it, then open it and it's fine. Spin it around, do something unrelated and it's all goofed up again. Patterning an assembly pattern also causes it to be confused sometimes and sometimes not.
If I save often it seems more stable, and anyway if it does crash it
>doesn't take as long to get back.