I've been an associate editor for the Journal of Environmental Management for about 2.5 years (I've handled about 160 papers). It has been quite the learning experience. I logged in today and found three papers that needed new referees. Examining the responses to my invitations, 1 potential referee had accepted, 7 had declined and 10 had been un-invited (i.e., had not bothered to respond to the email within 7-9 days). On these three papers I have an amazing 6% success rate.
What has been most surprising is the authors who will gladly submit one, or even two, paper(s) to the journal and then refuse to serve as a referee.
I am discouraged, to say the least.