OK, I can see you're looking for something other than non-commital answers. This probably won't help you much but my experience is this...
I signed up for iStock (because they inspect every image) last year, really just as an experiment to improve my photography. One thing you can be sure of with stock QC people is that they WILL tell you if your picture sucks, which if your skin is thick enough is way better feedback than 50 people telling you your image is "nice" on a tog forum.
I got approved with my second batch and made a sale within a week. I only have 87 shots on there but have learned more about the quality of my images in a year than in the entire rest of my life in photography. I currently sell one or two shots a day and even though the amount you recieve is laughably small it has bought me a body upgrade already.
Having attained a pretty consistent 100% QC standard, I signed up for Alamy a couple of months ago adding a few images each week. I've only got 57 images with them and have yet to sell anything.
I've learned a lot since starting this experiment, some of it you might not like to hear. But here are my thoughts;
Stock is not photography! There is often little art in stock, customers are looking for a message. Stock is more a discipline of marketing than photography, something born out in the terminology. I have taken some
pictures I'm really proud of and they will never sell as stock. I've recorded good
images which I feel absolutely nothing for that sell day in, day out.
I found it became an obsession, that I was constantly looking for anything I could shoot to sell and that became detrimental to my hobby. I also spent more time thinking about how to meet licensing requirements than getting a great shot. It can be quite soul-less actually.
If you have access to good models who will work for nothing, have lots of spare time to photograph subjects which maybe don't inspire you much, have a high boredom threshold then you can make it work but expect to put in a lot of effort. It would be nice to make a living from it but realistically....
Feel free to have a look...
http://www.alamy.com/stock-photography-search-results.asp?qt=stuart+hickling&ns=1&nu=0&lic=6&lic=1
http://www.istockphoto.com/spannerdude