I love backgrounds. I didn't even begin to use them until last fall, though. And now I see their possibilities. They add layers of complexity, and they can help make an avatar into a complete digital painting. (Just a very small one, lol.)
I don't really care what kinds of backgrounds they come up with -- I'm still experimenting, and I find all types useful. I'm kind of partial to intense colors and astra features, but I'm flexible. I just bought Crime Scene for it's black-and-gray rainy alleyway scene, and I love it.