I let friends borrow a tenner, maybe 20 quid from time to time when they have been skint, but that's about all I have done, and not let them lend anymore until I have been paid back what they already borrowed.
it just makes sense to limit what you let your friends borrow, it's not worth losing a friendship because of a money loan that was not paid back.
I have a friend, albeit one that I haven't seen for a few years who has his own carpet fitting business. as a favour to another childhood friend of his, he fitted his entire house with new carpets on the provision that he would pay weekly for it.
needless to say, after a few weeks of repaying the cost, things went south fast, and it ended up in court.
end result was that they never spoke to each other again, and my friend lost a lot of £ for it.
true story