My brother and I trade guns out quite a bit (he only lives a mile away, anyway...) and have for many years. As our kids are learning to shoot, he borrows the .22's a lot, lately, for example.
Beyond that... I have given a gun to my bestest friend (a worn HiPower) because I know his wife wouldn't let him buy one... so I GAVE him one. (He sold his dirt bike and all his guns when he got married because he thought he needed to become 'more responsible'... whatever that means.)
And I have a few rifles that I would loan, and a few that I would not. I did loan my AR to my TaeKwon-Do buddy when he was doing some security work in Houston after one of the hurricanes. No one is borrowing my pistols (get your own!)