I started pulling all my work from stock around 2 years ago. The value of either individual sales or use by large subscription deals had dropped to single digit dollar levels. At the peak I had four figure volume of work available for licensing through various agents. I was seeing images licensed for worldwide perpetual use by large publishers and I would end up with maybe one or two euros commission.
The other issue is what is known as a sub-licensing agreement whereby the first agent you can sign to ends up selling your work through other stock libraries. This means the 100% sale fee can be split twice or three times before you see your money. I
After pulling all images from stock the issues I have since found is that:-
a) Not all publishers using stock paid for it at time of download, and the agency never chased these up.
b) Even after pulling material from stock some agencies continued to license my work.
c) when contacted, none of those in either a) or b) think they have done anything wrong.
These issues have continued to cause me more problems than the original submission is worth.
As an aside, Getty are now allowing bloggers free use of images. There are rules and its not quite a free-for-all but the monetisation of this use is not as daft as it seems. Getty - who own the rights to the meta data describing your photo - can hang advertising alongside the image. As the entire process is based on meta data and its relevance to the advert, I don't anticipate Getty paying a share to the photographer any time soon...
So in summary, if you want to earn beer money go and work in a bar or stack shelves in the supermarket. By the time you have sorted, ID'd and described and keyworded your work the return on your time - not including the time to actually shoot the stuff - is so low you may just end up wondering why you bothered. After pulling from stock I have missed the 'income' precisely zero. It made no statistical difference to turnover.
And if you choose not to allow your creative efforts to be licensed by a third party for practically nothing then I will salute you.