I haven't followed him much. The consensus for a while started to be that he was really overrated. Apparently he was kind of inconsistent at USC. Some said he was a bit of a headcase. Some of his antics at the conclusion of his high school career (acting a fool after a dunk like he was the best player in the world) soured people on him. I remember Bill Simmons saying something (before they went to College) along the lines of Kevin Love being the exact opposite of OJ Mayo... one representing everything wrong with basketball today (Mayo) and one representing everything that is right (Love). People definitely started feeling like Derrick Rose was a much better prospect.
And then prior to the draft the Mayo hype started to come back towards the positive. A couple articles about how determined he was and how much skill he had. Talks about Miami desperately wanting to draft him (the rumor was that they were considering moving down so they could take Mayo instead of Beasley). Suddenly a lot of people seemed to think Mayo was the concensus 3rd best player in the draft behind Rose and Beasley.
Again, I haven't really followed him much. Have never even seen him play. But it seems he is still probably pretty inconsistent. The couple games I've checked of his preseason performance seem to suggest he'll have games where he'll shoot horribly and games where he'll go off for 26 points. I imagine he'll get points, but shoot something like 40%.