This guy is at best a decent bare knuckle boxer. Put him in the ring with gloves and a good boxer and he would get smoked. He has no idea how to work angles, has no head movement, and moves in straight lateral lines. Plus his cardio sucks he gassed in 9 minutes against Gannon.
FYI the 'UFC' fighter he was fighting against, Sean Gannon, had 0 fights in the UFC prior to fighting Kimbo. After the Kimbo fight Gannon fought 1 fight in the UFC and lost. Add to that Gannon was a Cop and lost his job because of the fight with Kimbo.
The basic deal on Kimbo is he is a big guy, can take a punch, and only takes fights in which he has a significant advantage. Would I want to fight him on the street? Not unless I had to. In the ring? No problem.
Check out some of Bob Sapp's fights and you'll see what happens to a big guy with marginal skills in real MMA competitions.
ETA: Bob Sapp vs. Nog: http://youtube.com/watch?v=jOPPldDIUVQ