I like the clean, minimalistic design. While the voice explains the purpose of the site quite nicely, you need a tagline and a clear written explanation as well: if the user doesn't see the value proposition in 3 seconds, they're gone (and what if they have their sound off?)

I also like the fact that you don't have to register to use your site.

I'm afraid the collaboration and social aspects are somewhat lacking - you should focus on those.

I can see the market for your site, but do you have a solid business plan to monetize it?

(long time fan of zombo.com)