I would do it if i had a second one to give, i was born with only one functioning Kidney but have never got the other one taken out.
I give blood, i am on the bone marrow transplant list and so i would of been more than willing to give up a kidney if i had one going. I've also done a bit of charity work for the kidney research foundation, and i really do think Kidney problems are some thing that alot of people overlook.
You can function fine with just the one kidney, i go out drinking every weekend and havent really had a problem with it. That said i could see why some one might be afraid of giving a kidney, but i'd think it was worth it safe in the knowledge you had just saved some ones life.