When orkut doesn't borrow features from Facebook, it gets inspired by other Google services. This time, orkut added themes, but not all the users can see the new option. The themes should be familiar, since most of them were created for iGoogle. When you select a theme, only you and your friends can see it in your profile page.
The unofficial Orkut Plus blog has some Greasemonkey scripts that could be used to see the new themes if the feature is not yet enabled in your account. If you notice a link in the header that lets you "change themes", then you have the new feature.
Since iGoogle's themes are really appreciated by users, maybe it makes sense to add themes to all Google services and change them from a central location.
{ Thanks, V-render Studio. }