Am I covered when I borrow my friend's car or allow others to drive my car?
Most policies cover occasional sharing of cars between friends. Check yours to be sure. If somebody else starts to log a significant fraction of your car's total miles, however, you should check with your insurance company. Primary driver variables can play a big role in determining premium prices, and providing false information can undermine the obligation of your insurance company to honor your policy.
Typically, insurance coverage "goes with the car." If you injure somebody while driving your friend's car, his policy will probably pay first. If he has no insurance, however, or if you are saddled with more claims than his policy can pay, your own policy should take up the slack. Again, it never hurts to check your policy or ask a company representative to be sure.
If your car is stolen, don't worry. You won't be liable for third-party damages caused by the thief, and your collision and comprehensive coverages will still cover damages to, or the loss of, your car.