Re shallwedive the request invite button is a bit off in ff - mid left of the email box. Works fine in the other browsers. It would be cool getting an awesome picture of the ocean as the main background (think flipboard).
To answer your question of what motivates me - vision and knowledge of what Steve Jobs once said, (along the lines of) - "what ever you see in this world was made by people no more smarter than you".
Impressive, but are they active? Google now makes you sign up for gmail and activates a google plus account even if you create a new youtube account. I think its youtube which is pushing it given more and more footage is being uploaded every minute - you need accounts to do so! and there's a host of other google services people are interested in too, so the line is blury.
But well done to Google anyway, still impressive signing up more people no matter what product.
Got to add a proper 'about' page which explains it - but Corsvi is a content discovery site which focuses on tech, formula 1, film, gaming and photography right now (whilst still developing ranking methods). If you think it would benefit from having more categories or anything else, do say!