I solved my problem: I had been playing recently with /etc/asound.conf following the last suggestion in http://forums.gentoo.org/viewtopic-t-732032.html , but apparently world of goo (and also some wine apps) didn't like it. Removing asound.conf solved everything for me.
I noticed that the ebuild of world-of-goo does not check for media-libs/sdl-mixer. Both my desktop and laptop needed that emerged for the game to work.
I don't know where the correct spot it for an ebuild-RFC... so that why i post it in this thread. Please tell me what the correct location is for stuff like this.