I only remember the first 45 minutes or so of my 21st. When you go out, try not to go epic big. It'll be epic, but just for the folks that will be making fun of you for the next 10 years. AtomicLabMonkey knows what I'm talking about.
Anyway, happy b-day! Have a good time out this weekend, and make sure you've got someone on nick handling duty so you have no worries getting back home!