DMickey, I agree. Although I really don't care what time my dd comes in, I like to know just for peace of mind. If she is going to come in at 3am fine, then I know she's not broke down somewhere. I suspect that this issue will be less when it's my sons. With girls you worry about creeps if they are stranded somewhere, or who give them a ride. That's actually the concern, not that they are out with their friends having a good time.
However, I have sons who are different then her. I still don't really have a curfew for them in hs, but I have to stay on top of things a bit more. Every time they go out I have to remind them that they need to tell me where they'll be and what time they'll be home. They never seem to know where they're going to be, how they're getting home, etc. I ask them to call me and they usually don't until 12 midnight, then they want a ride home. They often lose privelages over this. So because of this I reserve the right to be more parental if I feel I need to. Unfortunately, I can see this being worst when they are in college. If I have no limits at all they will be coming in at 5 am 7 days a week. Not OK with me. They're still good kids. Just more laid back about things, and really craving more freedom.
It's tough being a parent. You want your kids safe, but you want them to grow up and to do that they need more freedom. You have to set limits, but you realize that if they're too tight your kids will resent you and go wild, and not respect any of your rules. I'm always trying to walk the middle ground. In the end all we want are kids who enjoy their youth but grow up to be good adults.