Who May Drive Your Car
The rule is: the insurance follows the car. So basically, anyone can drive your car assuming it is with permission and that person is not specifically excluded under your policy (and "basically" assumes a standard "permissive user" policy—meaning anyone with permission can borrow your car). Insurance on the registered vehicle is primary, meaning if there is an accident with another person driving, the injured party will put a claim into your insurance carrier first, then go after the insurance of the driver if damages exceed the amount of your policy. Of course, if the driver of your vehicle is at fault, your insurance company will subrogate against his insurance company, meaning, seek compensation from them.
Okay, so you can lend your car to just about anyone, your niece, your rabbi, your 99 year old grandma. Why wouldn't you want to do this? Because it could cost you. Suppose your live-in girlfriend is driving your car, is not listed on the policy as a driver or as excluded. Well, your insurance company can charge a rate for her from the time she showed as living at your address until the date of the accident. Yep, you'll get a bill before the insurance company will pay out for the claim. And after the accident, they are likely to add or exclude her since they know about her. Also, another fall-out of lending your car, is if there is a severe enough loss, the insurance company could nonrenew your policy, and once your policy has been nonrenewed (even if you were a squeaky clean no accidents, no tickets driver), good luck getting with another preferred carrier. Insurance companies look at these things for 3 years: tickets, accidents, claims, and nonrenewals. So you could get with a preferred company after a nonrenewal, but you will probably have to be submitted for approval before the agent could bind coverage.
But besides these good reasons to practice prudence in lending your vehicle, there is this one: you can be held legally liable as the registered owner of a vehicle that harms someone else. And if your insurance and your driver's insurance aren't enough, you can get a judgment against you so you pay on that claim for years.
Enough scare tactics, don't mean to scare you. Everyone lends their car to someone, at sometime. So protect yourself, your insurance and your assets. Lend your car responsibly, consider the driver and the repercussions if there is an accident and act accordingly.