Hanson's old agency had some personnel issues, so he went and found himself a new one.
From mlbtraderumors: http://www.mlbtraderumors.com/2010/07/tommy-hanson-switches-to-scott-boras.html
Let me start by saying I don't have a problem with Boras, per se. His job as an agent is to take good financial care of his clients to the best of his ability, and he does that better than just about anyone.
Now that I've said that, a young player who is Boras client does not bode well for any team with a limited payroll once that player reaches free agency. All players are free agents at some point, so we'd still have to shell out some money to keep Tommy Hanson, but having Boras as an agent means 2 things: 1) Hanson will reach free agency at the earliest possible moment, and 2) the possibility of any kind of so-called "hometown discount" is pretty much zero. It also means that the Braves will now have to compete with teams that have much larger payrolls for Hanson's services upon his reaching free agency. Granted, this scenario won't happen until 2015, but the chances of Hanson remaining a Brave after that have become that much smaller, especially if he reaches his projected ability and proves to be one of, if not the most attractive free agent pitcher in the 2015 FA class.
Also, I'm not really sure if it matters much (or how), but Boras now represents 3/5 of the Braves starting rotation.