You don't want a .22 for self-defense, especially in the Northern US. In the northern US, it gets really cold-- so we dress in layers. Now, kevlar vests work because of interlocking fabric layers. With lower calibres, you can see a minor "kevlar" effect from the heavy jackets, etc. we have to wear.
Thats not saying a .22 shot in the chest or abdomen with a thick jacket wouldnt kill the target. A .22 in the center of mass, even slowed by a jacket, will ruin a bad guy's day-- but it might not kill him right away. Someone earlier said that when you're using a firearm in self-defense, and especially a handgun, it better be because you want the guy to stop whatever he's doing RIGHT NOW. A .22 slowed by a down parka, vest, sweater, and a couple of shirts might not stop him right away. So, soon as I turn 21, I myself am going to register for a permit, and probably get a .38 or 9mm. Its the duty of every American man to protect himself and his family.
IMHO, you don't shoot a .22 in the center of mass. There are three areas to pick: nose, and both eyes (assuming a head on shot).