Clumsy web design speaks volumes about a site, and reflects nicely the amount of sales you will get from this one. Three different logins for affiliates, buyers and photographers, poor commission, and not a lot of traffic, infact alexa does not even rank them in their statistics.
I'm not boasting here, and I was shocked to find this out, there is more traffic to one of my travel photo sites that this and the site in question (which i am disclosing the URL of deliberately) is by no means one of my most popular!
verdict: 'microstockphoto is out of the running by a mile'
Update JUL 08: after 2 years, zero sales, and the unexplained loss of almost all the images in my portfolio on their site, I am no longer monitoring microstockphoto.com