My initial thought is that white can reply to b5 with e5, severely hindering your kingside development. For this reason, normal is at least to play Nf6 before dxc4, so that after white plays e5 your knight may develop to d5.
Note also that White is not obliged to play e4 immediately after your capture. He can play a4, and follow up with Nc3 and e4 at his leisure.
Black has the nice b3, or can attack the pawn chain with a4. I've studied these lines a lot from the black side and the only way to play this way soundly is the Noteboom variation. Basically, instead of taking the pawn right away, you play e6 (to allow Bb4 to pin the Nc3 knight), after Nc3 then you take. It's actually an amazing defense to play for a win from the black side vs d4.
Here's a good webpage on it.
http://jaxchessnews.com/id74.html
Here's about the opening you bring up : http://jaxchessnews.tripod.com/id70.html