I think the Bulls reached on that pick. He looks to be solid, but I don't believe he develops into a star. However, he can be an ingrediant ina championship caliber team, and that's what I think the Bull were aiming for.
Part of the reason they traded J.R. Smith and picked up Griffin was to have a veteran who can guard the bigger two guards (Lebron, Kobe, etc.), who has respect with the officials and won't get into foul trouble quickly. Griffon will be used to play the two as well as the three, and Thabo has been having a great summer league and is expected to get minutes.