There's definitely room in the market for several players (in terms of the whole crowd-design/manufacturing space), but I think that down the road, there will be one clear winner. At the end of the day, this industry is a network effects game. Inventors/sellers will always flock to the service with the largest user base to increase their chances of getting their ideas to market. Right now, I'd say the frontrunners are Kickstarter and Quirky, although I've personally seen inventors shy away from Kickstarter because of their increasingly stingy policies. Quirky probably has the most unique model by partnering with big box retailers and tapping into a much broader distribution bottleneck.
The site itself is a bit weird. Most of the content looks like it's loaded in via AJAX, and on a slower connection it's pretty jarring. Clicking on "See All" initially shows the "About Us" section of the page, which caused me to think I clicked the wrong link, and went back. It wasn't until I clicked it again that I noticed what was going on. At least throw some kind of AJAX spinner/placeholder or indicator that the page content is still loading.<p>Cool idea though.
Sounds like a great concept. But 35% of markup is too high. Margins for hardware goods are low enough already. Then you take 35% of that. I think you'll end up with a bunch of overpriced items with inventors struggling to make a profit.
I don't mean to be a yes-man, but just to offset some of the other comments: The site is clearly an early (but totally functional) version. It will get better + prettier + more ajaxy as time goes on. Bravo on your launch!