We tried it, and it works as advertised; since our kid is a pretty smooth eater, though, our results aren't terribly dramatic. Digging and asking around, I've found something of a cult of Dr. Brown's; apparently, it changes the lives of a lot of colicky kids and fussy eaters.
How does it work? Like any other vented bottle, the goal is to cut down or eliminate the air bubbles a baby takes in. Brown's does this with a sieve under the nipple attached to a vent that sits inside the bottle like a fat, Pulp Fiction-style syringe. One caveat: although it comes with a little wire scrub brush, the tiny openings might be a pain to clean without a dishwasher.
They're for sale singly for around $7, or you can buy a 3-pack of Dr. Brown's bottles at Babies R Us/Amazon for $12.99