If a criminal uses a gun, the victim will just take it away...
When I interviewed Prof. Gary Kleck for the documentary, he observed that there is some manner of urban legend about people using firearms in self-defense, and having the criminal take the gun from them. He hadn't found a single case of this, and guessed that it might arise from cases of law enforcement being shot with their own gun -- since LEOs are often forced to grapple with a suspect, or escort them around, while their gun is holstered and thus available for a grab.
Clayton Cramer has just blogged a case where the victim took the gun from a robber. The robber stopped to rifle the victim's pockets, and the victim got the gun away.
The other day I saw a store security video, pretty funny, where the robber comes in and presents the gun in an overhand sweep, with the other hand coming up to make it a two-handed stance. He does it a bit too dramatically, and apparently gripped the gun too loosely, so the gun popped out of his hand and landed on the counter. The clerk moved quick and grabbed it, and the robber turned and ran for his life.
I'd suspect that "victim grabs gun" is a lot more frequent than "criminal gets gun away," since (1) a victim needs worry about taking on the criminal, while the criminal has to be concerned about retaining control, getting the loot, and watching over his shoulder for police and (2) the victim is rarely drunk, high, or really stupid.