I'll be doing it soon.
Looking back I haven't done lots of things I wish I had have done by now. Stuff like live and work abroad for a year, have a string of short term flings (been relationship-ed at key points of my 20s). My career is meh.
I haven't even learnt to drive yet.
Those who are 30+ did you see it as a marker in your life? Did you vow to change anything?
Also, how did you celebrate? Big party with literally everyone you've met to show you're a somebody? Or did you let it slip by without a fuss?