It feels like a cross between what deviantart would be if it had quality control for promoted images, and dropbox.
On one hand the generous account space is nice, but from what I've been able to find so far on the site, besides the community sharing images publicly with everyone, it seems to fulfill the same role as dropbox does.
The ui is nice, and I could see myself using this for images that would get my dropbox account temp suspended because of the bandwidth limit, but besides that, I can't really think of any reasons why I'd want to use this over dropbox.
Either way, the site seems to be fairly popular (from what I can tell), and you definitely get brownie points for actually going out of your way to support tf2 map development. I'll keep an eye on this to see where you guys go from here.