The site looks fantastic, great work. Have you looked into sketchflow? It's kinda/sorta a competitor, and kinda/sorta something you could incorporate into your site. I could see a demand for a nice, easy, secure place to host sketchflow mockups. All they require is an html page and a silverlight xap bundle. (sketchflow is bloody fantastic btw, I think it's going to make some serious inroads into how people make mock ups)
