Pretty much a common sense situation here again.
I let my friends borrow gear all the time. Just tell them up front what the requirements are (date you need them back, if a head is jacked up they replace, cymbal crack they replace, etc...).
Dude, if their your friend, by a friend!
I'm down with what Sabe said about the contracts if you don't know them. But why the heck would you loan out gear to someone you don't know?
Common sense! If they suck, NO. If they are under 18, NO.