Sounds like he swapped good charges for lesser charges which had run the statute, but had to waive the statute to do so. It appears he also has to pay a sizable fine and cooperate with the Feds. (The latter feature could have some non-monetary risk, but then he is/was in the security business for what that is worth.
Obama arrest, Justice Department protects Obama, White House insider?, Blagojevich Rezko Obama
One comment posted suggested this is linked directly to Obama when he was the Chairman of a IL State Senate Committee back in 2003.