I just celebrated my birthday at Disney World over Labor Day Weekend and posted a trip report! It was the best vacation my husband and I ever had (maybe leaving the children at home had something to do with it...).
All the other posters had great tips. If you wear the birthday button, then CMs and guests will be wishing you "happy birthday" all day (or weekend, in my case) long. I felt like a princess from all of the attention. I received a treat at every meal (we had made several PSs), and often a song. I was even invited to lead the parade at the Crystal Palace! It is a WONDERFUL way to spend a birthday!!!!