Here is a sheldon page on brake compatibility. This is a primer on why you can't just use v brakes with STI levers. Here are a few reviews of the travel agent. I'm a little leary of it to be honest even though it is working fine presently. We've not had a ton of rain yet so my dirt level is definitely low. It doesn't seem like a permanent solution and I'll probably go to the BR 550s eventually. Here's a photo of the device from a bike shop web site. It takes the place of the "noodle" in a v-brake set up.

It's funny but if you check out the 2008 tri-cross you'll see that Specialized actually developed their own v-brake to work with STI shifters and ditched Avid shorty brakes for that year. I tried one out and was impressed. Couldn't afford the bike though. Not sure of the longevity of such a set up either. Oh well. Live and learn.