I had a very similar experience to PreDent below. I graduated a semester early simply because I was finished with everything and didn't want to waste money (I didn't really try to have my classes done, but it worked out that way.) It was nice to have a full 8 months before dental school, but I had NO idea how much I'd regret not having that last semester to have a bit more college and fun time.
Dental school is NOTHING like college...I'm a first year now, and it has its own joys and challenges, but you will not be reproducing your experience at undergrad, regardless of how close you are with your d-school friends. College was just so free and relaxed and social....there will be a lot more older/married people in your class in dental school, and you always have so much to do that even with a balanced life you have less free time. I couldn't have justified spending money on that last semester, but if I had known beforehand, I would maybe have spread out my courses more. OR, at least I would have stayed living closer to my undergrad (I was around 30 minutes away) and hung out with my friends more, or worked at my university.
It's funny....the counselor here said that the number one complaint for freshmen was homesickness, and we all looked at her like she was crazy. Turns out, even the people that went across the country for undergrad end up being a bit lonely in dental school...there's something about giving up your last bit of being a "kid" perhaps.
And it wasn't raised in any of my interviews...I think they're mostly concerned about your first 3 years.