Brain Stuff - How does bilingualism affect the brain?

Psychology, more than most sciences, gets to make an appearance pretty frequently in popular media, and this particular notion is a favorite - that speaking multiple languages does things (these days, usually good things) to the brain. Every few months a study makes waves in the news, and like most science journalism, it usually involves hyperbolic headlines surrounding what's really an incremental advance in an ongoing and complex debate. There's definitely not a conclusive answer yet, but it still seems like too noteworthy a topic to pass up, so I'll do my best to represent the current debate.

A bilingual Hebrew-Arabic classroom in Israel