A gentleman asked me today during the setup time of my SEO for ASP.NET Developers presentation at Central Ohio Day of .NET about changes to theming in Community Server 2008. I said that I had just recently seen a couple of posts from Ben Tiedt show up in my feed reader about that very topic but that I had not read them yet.
It looks like Ben is doing a series of posts about themes in CS2008, you can catch the introduction and links to the other articles here.