I currently have about 2100 clips at two major sites (SS and P5). Almost all of those have been shot within the last 15 month - and I do have a full time day job that has nothing to do with footage. It's just a matter of dedication to aquire a gallery that size - obviously having a store room filled with tapes from decades of shooting will help, but it's not neccessary. ;-)

Income? Well, I can't compete with Francois, but last month gave me $600 distributed over all sites (plus some from photos).

I have tried IS - got some 500 clips there. I found the upload process extremely tiresome and the reviews extremly slow (they had good weeks, too). While I sell more clips there than anywhere else, I still make a lot more money at P5 and SS.

You really need a gallery of considerable size at SS to see consistant sales, but it's sure worth going for.