I've always slept with my contacts in. My very first doctor when I first got contacts was like "in a few days or whatever when you get used to these things, you'll be sleeping in them and it will all be natural." (This was as I was struggling to even get the dern things in to begin with.) It was only my last eye doctor was all shocked that I didn't take them out at night. So for a few months, I started taking them out at night. Then I got a better job with better hours, but one that didn't give me as much time in the morning, so it was right back to sleeping with them.
Anyway, I've had this pair in for a few months now (admittedly too long) and they've maybe been out once or twice. It's my last pair, though, and my prescription ran out (er, uh, in 2007).