I started submitting to Alamy.com in 2003, the stock library which currently (February 2012) holds more than 28 million images. My meagre contribution stands at about 5,600 images, but slowly growing. In the first few years of my participation I uploaded lots of travel pictures from many different locations and the money return was fairly decent. In recent years that has diminished through dilution by the number of photographers and the quantity of images, deals done with publishers (led down that dark road by Getty) and the ubiquitous worldwide recession. Of course, the prices offered by iStock and it's microstock lookalikes were a major hit in the pricing of stock images.
Many of my compatriots whom I know through various stock forums submit to multiple agencies as well as Alamy and also have their own portfolio sites where they market from directly, but I decided early on to stick to Alamy alone. Firstly I felt that my stuff was too generalistic in subjects and not particularly conceptual - actually a rag-bag of images, so the logical home was Alamy, which does not edit contributions for content. Secondly, I had had my fill over the years of the business of photography. I no longer wished to market myself or get involved in accounts.
So there it is - I am now a happy hobbyist, albeit with years of photographic experience in his back pocket.