I went to my 10 year one, 6 weeks after DD1 was born.
I was bullied quite badly in school in the sly underhanded excluding you type of way that can sometime happen in girls schools. By the people who were meant to be my friends.
Half the reason I dragged myself to the reunion was to show those particular girls that I had survived (in their eyes, I was the brainy, plain one whose job it was to never have a boyfriend and explain the homework to everyone - and over the 10 years I had realised that I was smart, ambitious, attractive and they couldn't keep me in their little box).
I wouldn't say I enjoyed it, but it was nice seeing them react to me blowing their misconceptions out of the water (stayed at home since school - nope, lived in the Far East and travelled extensively; single - nope, engaged and with 1 DD; fat and plain - nope, slightly chubby since giving birth, but otherwise looking amazing and confident)
I also discovered that quite a few people who I had liked but who I thought didn't particularly have time for me, actually liked me quite a lot (or at least seemed to, and made a beeline for me to talk to me).
That said, it did bring back a lot of bad memories and I'm not sure I'd do it again.