It seems that the totally new default theme for ubuntu that was going to be released in the Hardy Heron version has been deferred to the next release (8.10) that will be out on Cctober.
You can take a look at the some theme concepts that can be found in the Ubuntu Artwork Wiki. And take a look at one of the most popular theme, Gelatin, made by a Brazilian.
Ubunt 8.04 won’t have a totally new visual style (but they will change somethings), but they said that’s because ubuntu developers want to focus on news features and improvements.
I personally prefer to have system improvements then visual themes, even that I like theming my Ubuntu. Some of the new things on the next ubuntu version:
Via [tombuntu.com]

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