Mid mentioned something about the custom backgrounds exclusive to the Supporter accounts, mine is an example of the nice customization features that are exclusive to Supporters.
I've been a Supporter for almost 2 months, but I didn't always have a 5 on my Supporter's userbar. It was a 4 when I first got it but then it suddenly became a 5 when someone donated $5 to me. (I won my initial Supporter status from a competition, through another user giving it to me as a gift)
If you have the ability to donate, you should consider getting Supporter status.