Years ago I loaned out a really nice tow bar, never saw it again. Between that and some other stuff that happened made me not want to do loan anything or get involved in any kind of project with other people for a long time.
That said, I have one long time friend who I will loan anything to and help do anything he needs a hand with. Recently I loaned him my TIG welder. I bought the welder 20 years ago, partially because I wanted one, but also to put a rollcage and a backhalf kit in his 68 Camaro. He bought the argon bottle to go on the welder. A few years ago he bought a Bridgeport mill and a lathe. I brought over my gantry crane to help him unload them and gave him some accessary stuff for the mill. I have since racked up many hours on the lathe and mill making stuff I need.
As was said above, you need to be very selective about who you hang with and do stuff with, there are lots of people out there who have no problem taking advantage of you in any way they can.