Depends on when different people are used to going to bed, how much sleep it takes for them to feel like they've had enough etc though.
For example myself, unless I'm REALLY tired going to bed before 11pm is pointless, because I've tried it several times and it always takes me at least an 2 hours to get to sleep if I go to bed before that time.
Furthermore for me, the longer I know I've been in bed trying to get to sleep but still being awake, the more I think about it, making it even more difficult for me to get to sleep. So I'm actually likely to get more sleep if I go to bed at around 11:30pm than I would if I went to bed at 10pm!
There's also the fact that whilst I'm awake I like to make the most of my time and unless I really feel I need the rest I see "extra" sleep as wasted time!