It seems indeed "bone-headed" to have allowed a shady character like Tony Rezko anywhere near you. At the same time, I'm having a hard time seeing anything substantively damning of Obama in the story. TPM:
And then there's the other big question, whether Obama ever did anything for Rezko in return for his purchase of the side yard or all those contributions. Obama has said that Rezko "never asked me for anything" and "I've never done any favors for him." No substantial evidence has surfaced to contradict that claim.
Barring anything we don't yet know, that seems to me to be the critical point.