I think that this approach is reasonable enough, but I'm skeptical that it will actually prevent the unauthorized posting of material to Scribd. However "fuzzy" the Scribd text-matching is, it's likely that determined pirates will figure out how to exceed its threshold and get around it. And it's also unlikely that Scribd's database will ever comprise a significant fraction of all copyrighted works. Finally, it's easy to imagine that pirates could have the best of both worlds by posting material to other web-hosts that don't have the text-matching in place (that is, every web-host except Scribd, from your local ISP to LiveJournal, Blogger and WordPress) and then posting files that link to those hosts on Scribd.
The good that this will do largely revolves around people who aren't sure if the material they're posting is or isn't in copyright -- these folks will be notified that the works they're posting aren't kosher. So there's some good that comes of it.
Scribd has been unfairly targeted as a haven for pirates, a company that relies on infringement to line its pockets. The reality is that Scribd is not anywhere near the top of the list of sites that end up hosting infringing material. Any site that offers free hosting to the public will have infringing stuff on it -- for example, LiveJournal, where the Science Fiction and Fantasy Writers of America host their public conversations, has far more infringing works (photos, texts, etc) than Scribd does -- naturally, as it is much larger than Scribd. Flickr probably runs neck-and-neck with them. YouTube dwarfs all of them.
Scribd has also been accused of being obstreperous in its removals process -- again, without any basis in fact. Every hosting site has a near-identical procedure for removal of material: you fill in a DMCA "takedown notice" in which you swear that you're the rightsholder or an authorized representative, and they take the material down. This process is unfairly characterized as burdensome, even though this process allows rightsholders the power to have material removed from the Web without showing any evidence that there's any infringement going on.
Compare this with the offline world: if you believed that a bookstore was carrying an infringing edition of your book, you couldn't just walk off the street, sign an affidavit swearing that the book was really your work, and expect the bookstore owner to take it off the shelf (for starters, this would be a disaster for free speech, as every axe-grinding yahoo would be able to get books censored just by filling in false affidavits). No, you'd have to hire a lawyer, go to court, prove a case, and then the work would come down. When you unpack the claims of SFWA members who had material removed from Scribd, the complaint amounts to, "They made me swear that this was my book before they removed it."
The process for removing things from the Web isn't burdensome. It is so easy that it is frequently abused -- everyone from the Church of Scientology to Diebold have used takedown notices to silence their ideological opponents by falsely claiming to have been infringed upon.
Scribd is trying to find something that will make SFWA happy, but the members who bruit about the shibboleth that Scribd is an extraordinary bad actor are not basing their claims on the reality of the situation. Scribd is no different from any of the services that SFWA members use every day, from Google Mail to Blogger, from LiveJournal to Flickr: a commercial entity that provides a low-cost place for the public to express itself. Every one of these services is abused by infringers, and every one of them has exactly the same procedure for addressing infringement.
Indeed, Scribd has already shown its willingness to set aside the law and take extraordinary measures to make SFWA happy, as when it honored a malformed and sloppy "takedown notice" sent by SFWA Vice President Andrew Burt, one that listed dozens of works that Burt did not have the authority to represent, including several that were under Creative Commons licenses (including my own first novel, Down and Out in the Magic Kingdom).
Apologists for this claim that no real harm was done, that the ill that arose from it was that my book "was unavailable from one source for a few days." This is far from the truth: when SFWA had my work taken down, it caused many of my readers to believe that I had abandoned my commitment to free sharing of my works and to write to me accusing me of being a hypocrite, swearing never to buy my books again, and so on. Only by publishing the facts of the matter -- that I had not caused the book to be removed, that SFWA had acted against my explicit prohibition on their acting as my representative for copyright claims -- was I able to communicate to all the people who'd seen the page saying my book was offline because copying it was prohibited that I was not behind this.
The good news is that SFWA's Copyright Committee has a new chairman, Russell Davis, whose public notice on assuming the chair are very heartening and promising indeed. Link