Like the MyKindex site which operated for a period of time last year, MBC connects authors with a willing pool of book buyers. The site looks to be entirely author funded, and from what I can tell as a reader it works along the same lines as the services that sold reviews to authors like John Locke.
A user signs up, request to purchase a book, and after the purchase is verified the user is credited the price of the ebook plus an additional 30%. After a user buys enough books to pass the minimum payment threshold, they can request a Paypal funds transfer.
Or at least that is how the site is supposed to work; I just signed up today and I am still waiting for the credit for the ebook I bought. It's a $.99 title in the Kindle Store with 4 five star reviews.
It's not clear yet whether this site will have any effect on the Kindle Store best seller list, nor does the site claim it can do that. Instead it merely says that it connects readers to new authors.
But the site operates in a shady manner, and I learned of it via the developer of My Kindex, which did boast of manipulating the French Kindle Store's best seller list, so I am more than comfortable with attributing nefarious goals to this otherwise nondescript site.
My Buying Community claims to have 10,000 members, and if that is true and the site marshals all of its members to buy a single title then they well could affect that ebook's rank in the Kindle Store.
Hopefully Amazon is already aware of this site, and is taking steps to thwart it.