In order to promote the game when it will be released in Europe, 2D Boy might consider making a partnership with the (awesome) website LaFraise.com. At least in France, I don't know the popularity of the website out of it.

LaFraise, it's a permanent contest of tee-shirts design, and a lot of amateurs (but very good) - or not - graphic designers permanently participate on it. And - very often - there is a partnership between LaFraise and an other enterprise/foundation/organization to design one or more teeshirts with the brand/universe wanted by the partner.  :P

LaFraise is very popular in the graphics and computer geek French communities and is becoming really more and more famous to ... normal people. Some games (Little Big Planet, the new Space Invaders ...) have already have their contest on LaFraise. Visitors vote for their favorite creations, but it's the partner who choose the final winner.  :)

And I'm sure that the LaFraise team should love World of Goo ! ;D I don't know the price to become partner, just the time during a contest, but 2DBoy could ask information about it ... I think it would be very nice and in the WoG mind continuity.  ;)

I am a fan of Lafraise.
I have bought plenty tee.