Woah...some play some serious hours! Longest I've played LFS must been 4-6 hours, I don't really know, but I can't play it long as other games. It must be the focus and work you need to keep up.
I remember once doing two longer races in one evening, the other must have been something like an hour plus quali, and the other (OLFSL event) a bit more (could have been a lot more actually). I did about 650 km that day on those two events, plus some practice, and it was all in the FOX. I felt totally horrible and exhausted after the second race, never have felt like that after playing some silly game!