I have not put a huge amount effort into being accepted to sell microstock photos on iStockphoto, but the attempts I have made so far have all been for naught. Obviously each microstock site has its own process for being accepted as a contributing photographer, and some are easier than others. Shutterstock turned me down the first time I tried, then accepted me on my second try. I don't recall having any problems getting accepted at Dreamstime, although I also haven't done much there and have only made a couple sales. I also don't recall having any problem with FeaturePics, which (to date) has not resulted in any income. But iStockphoto... they've been a bit challenging. I'll keep working on it, for now at least. Wish me luck (or skill, I suppose).