I buy a ton of them, I've probably put in over $1000 into DLC. There's a stack of nearly 30 points cards on my desk, along with the occasional credit card fueled points add at 4am for overnight gaming. 
 
Especially with bigger titles like the Penny Arcade series, Shadow Complex and Battlefield 1943, there's a huge future for XBLA that I'm really excited to be a part of.