Cool info - definitely didn't know that... I thought it would be similar to what a Gurney Flap does, but in looking at Coanda info, you're probably right. Here's some Gurney Flap info for those who aren't familiar with the tech:
http://www.insideracingtechnology.com/tech104gurney.htm and
http://www.allamericanracers.com/gurney_flap.html
Either way, I'm sure it's a functional piece which BMW didn't just put there for looks, so I won't be removing it
