In SL you can be who you want to be. You can experiment with your appearance in a way that is impossible hair, skin, shape, and gender are all variables. A change of clothing is only a click away. If only it was so easy in the real world!
Despite all these possibilities, I have to admit that my avatar is quite boring. I have had the same clothing on for nearly a year now. I think my linux t-shirt must smell a bit by now.
I have a couple of avatars in different projects, and on the teen grid adult educators are locked to one island at a time. So even through I have to use differnt avitars, I have tried to keep the appearance and clothing the same in each of the Islands.