I actually didn't celebrate Purim growing up so in a sense I'm coming from the other end. I went to a klezmer purim jam session, and then had a nice lunch with some friends. I shared hamantaschen with my co-workers, but no costumes.
I'm a big believer in just being Jewish in public and having a great time with it. Too often I used to keep my Jewishness to myself and it often meant people only found out I was Jewish when it was inconvenient for them. Being proactive means people learn about it while eating cookies!