I tried to sign up to SS last week but ran into a snag. My desired user name, my real name and my email are already listed as a member of Shutterstock. Since I have never been a member before this confused me so I used their sitemail forum to send them a note trying to figure out what's going on. However I have not received a response. Not even a "we got your message we're looking into it".

How long does it usually take for support to respond to a message?

they';re usually pretty reasonable -- a business day or so. 

i've had similar problems with 'cascoly' being 'already used' -- in one case it had kept a signup from several YEARS ago.  try to sign in with the name you want and ask for the password to be sent -- you may find out you'd forgotten you'd signed up.

I hadn't thought of that. I don't remember ever signing up with the site. I've got my first 10 in now so we'll wait and see.

Similar problem, my username was "already in use" as a buyer, so I couldn't get it as a photographer. OK so I took a different name. I don't understand, but I'm not going to fight the system. Too lazy. 
I'm pretty sure that I'm the buyer registered with that user name.