What a great idea to start a thread to celebrate the thirties (don't worry, I think this one is a little more cerebral than the vagina/penis celebrations!).
For some reason, I honestly didn't have a tough time turning thirty, but as I progress (almost 34) it gets a little scarier. But one thing I've noticed in looking back at my 20's is that back then, it was very difficult to look at things like politics, religion, love, life choices without getting riled up and excited -- like I was going to change the world just by being passionate about something. Now I realize that I can be still passionate and aware without all the adreneline and in the process am understanding things a *little* better, at least. I'm able to listen to other people, other views, and actually appreciate them a lot better than I could when I was younger, whether I believe in their views or not.
And I love littlek's bit on being "sexy" rather than "cute." I love that part about being older, too. When a younger guy hits on me now (it does happen once in a while!) and then finds out that I'm 10 years or so older than him, I've noticed the facial expression changes from that of a guy looking for someone to go home with to that of a guy who is admiring a really fabulous woman that he knows he couldn't possibly match up to.
The bad part is that you will *have* to start working out within the next few years, if you don't already, and oh yeah, the mental thing that sozobe mentioned, but it honestly is more relaxing, more sexy, more life-affirming than the twenties.
So don't stop being the "cutie" that you are, just realize that it may come off as "sexy" instead -- or that your views will probably be taken at least a little more seriously than they did a few years ago. Congratulations and welcome to the club, Anastasia!