NANPA member Charlie Borland has posted a good analysis of the lack of monetary benefit for nature photographers thinking of contributing to microstock sites. Here's the link: http://www.pronaturephotographer.com...ers-to-crunch/. I have to agree with him that the numbers just don't add up.
In addition to Charlies post I mentioned earlier, there is a good discussion, called "Two Tier Pricing" on the Stock Photography group on Linedin right now at: http://www.linkedin.com/groupAnswers...k=.anh_1541417.
Jim Pickerell contributes a lot to this discussion and it's worth a read if you shoot stock and are concerned about the direction of stock prices.