Harlan Ellison Breaks it down from the writers point of view. I'm sure professional musicians agree.

http://www.youtube.com/watch?v=mj5IV23g-fE

While we're on the subject..

A pretty good read..

http://sivers.org/book/IgnoreEverybody

I think it was Scott Englebright that said this to me:

When you take gigs for free or even less money than someone else, you are setting "the standard" for everyone else.