I lent my car car to my sis and her hubby for 3 weeks when they were over from Australia. Put them on my insurance etc. I would do the same for a trusted friend I think.
To be fair my car is an R reg fiesta 1.4 so not of great monetry value, however I do rely on it heavily (wasn't easy going without it for 3 weeks!!) so I wouldn't just hand it to anyone, I'd neeed to feel confident that they were reliable drivers!