OK - here's the thing. My kids were on a schedule. A bit less so now that they're 6 and 7 but they still go to bed between 8 and 8:30. I know a ton of people who were schedule-less and honestly if it works for you and the kids aren't overtired or whatever due to staying up til all hours, it is fine.
A couple of comments though:
1) When you invite over friends for a 'glass of wine' and then your kids are up with the adults and the Disney CHannel is on and then they get overtired and are crying at 10pm - this is not fun for those you invited. Don't get me wrong- if you invite my FAMILY over - no problem. But if you invite the ADULTS over and I get a sitter, I make the assumption that it is an adult evening and don't really enjoy getting the opposite. I love having my kids on a schedule so that I CAN easily invite adults over for some 'grown up' time after the kids are in bed.
2) If you choose to let your child go to bed 'whenever he/she is tired' that is fine - but please don't act like those of us whose kids go to bed att 8:00 just 'happened upon' kids who miraculously go to bed on their own early. This was work and discipline to get to this place. I get so many 'WOW - I WISH I could get my kids to go to bed like that!' comments ALL the time (esp. when they were like 3 and 4). And I'm like 'well...you ARE the parent, if you REALLY want it, then you can do it (with time and effort and discipline)'. So while I don't have a problem for those who really DON'T want this. Don't just let the kids go to bed 'whenever' but then complain and 'wish' that it was otherwise - it IS in YOUR control to do so (in most cases, I'm sure there are special needs, etc. when this is not the case). And, IMO, if you think that at sometime in the future you might want this - it is MUCH easier to start at a young age.
3) Babysitters LOVE working for me!

I know many neighbors they do not say 'yes' a lot for. My kids easily go to bed, know the routine, and the sitter then gets paid for watching TV for a couple hours after.
4) When I'm not feelign great or just had a bad day - those extra hours I get when the kids are in bed are invaluable. Just to veg OR to go to bed early myself. I can't imagine having to stay up with them on some nights!
5) Our high school bus comes around here at 6:30...I figure my kids will no longer be going to bed at 8:30 by then - but really - many high schoolers I know go to bed at 11 - 12. Now I'm not to this point yet but my current thinking is that this will NOT be the norm in my house. I really think most kids in order to perform their best, need at least 8 hours of sleep. So it's good that they know now that I determine the bedtime - cuz I still want it to be reasonable when they have to wake up at 6am on weekdays.
I still remember my good friend coming over when dd was about 9 months or so...and hearing her coo and talk in the baby monitor my friend said 'oh - doesn't sound like she's tired, can i go get her and bring her out to play?' and I said 'How am I ever going to teach her that 8:00 is bedtime if I don't actually have her go to bed at 8:00?'. So I started early. Is it always perfect?? NO WAY! We have our 'scared' nights and bad dreams and the rest. But the majority of the time it is VERY GOOD.