i just saw on n4g that you get a free game if you download a theme and redeem the code on your Go. this might be only in europe, but i've read some comments that it applies to all countries. if anyone can confirm the latter statement please post.
source: http://blog.eu.playstation.com/2009/11/30/get-a-free-game-with-pspgo-happy-holidays/
source: http://blog.eu.playstation.com/2009/11/30/get-a-free-game-with-pspgo-happy-holidays/