The only car I've ever borrowed has been my mom's, and not really borrowing per say, but using it to run errands for her. When she moved in Oct, I rented one one way, and we drove up in hers. The couple days in between me arriving and the move, i used it to run errands, and also have done so in her new place. Being in a wheelchair, she can drive, but it takes longer for her to get out, in the car, get her chair up in the car topper, etc. So sometimes its just easier for me to zip out and do what needs to be done.
I'll be taking her car sometime in the near future, as I need to get it inspected for her, and due to the way they do it, she can't. But no biggie.
I don't loan my car to anyone except for Mr. Sirius, but he's on the insurance. I also don't like to drive his car even though I'm on his insurance. I'd feel terrible if I got into an accident while driving his car, whether it was my fault or not, even though both of our cars are 20+ years old and he's the only owner his car has ever had. I don't like driving it anyway; it has a very stiff clutch, whereas he complains that the clutch in my car is too spongy. I guess it's just a matter of preference.