I have to admit I have a couple of issues with him that just nag at me. First, his lack of memory regarding the organization he was proudly a member of during the 70's at Princeton. He was proud enough of his membership to include it on a resume in 1985, so where's his pride now? I don't buy that he doesn't remember, and I don't buy that he wasn't an active member, either.
Secondly, his failure to recuse himself from the Vanguard case until he was called to task on it after the fact. I heard a bunch of paperwork mumbo-jumbo, but it boils down to this: He was briefed on the case, he knew there was a potential conflict of interest, and he opted not to recuse himself. "The clerk didn't give me the paper to sign off to recuse myself" is not an excuse for breaking his word to the Senate that he would not sit on a case involving Vanguard.
I don't suggest that this would be enough to constitute blocking his nomination, but it would be better, IMO, if he'd admit to making some mistakes instead of using selective memory and technicalities to attempt to make himself appear flawless. I'd feel more comfortable with someone who can admit to making mistakes in the past and having learned valuable lessons from them.