I am well aware of its use as an assassins weapon. The problem with a .22 though, is that if it doesn't hit one of those "instantly lethal" areas, it is just a nuiscance to most. Sure the person may bleed to death later, but in the mean-time they are not likely to be debilitated in the least (though a certain percentage of people are indeed dropped by any round that hits them anywhere).
Possibly, but consider that many attacks are stopped by the mere brandishing of a gun. Things will happen so fast that the perp may not know how hurt he is, and may not realize that you only have a .22. If this happens to be a mugging or the like, i'd bet in 9 times out of 10, the perp flees. If this is some altercation where the person is dead-set on killing you, then I may lean towards your opinion.