One of the main reasons I'm optimistic about the idea of backgrounds and themes is that they seem to disconnect feats and skills from classes and if that is really the case than its a good thing in my book.
Warder
Im good and bad on this use of themes.
One the one hand it provides a very versatile mechaism for character definition that is easy for players to latch on to an conceptualize final intended result.
On the other hand, if this is what themes are what you do outside of combat it sorta dooms classes to be what they do inside of combat. Its what the classes end up being that would worry me in this scenario. Take the theif example, would we end up with "Theme:Theif, Class:Agility based knife fighter"?
I think classes should remain the core defining aspect of character capabilities both inside and outside of combat, where themes are extra color with extended capabilities.