Googling around, I have come across quite a lot of material I wrote on the Scribd site, including a sizable chunk from this blog, a sizable chunk from the Miscellany (a book my wife and I wrote and self-published on our medieval hobby), the full text of several of my commercially published books, and what appears to be the full text of translations of my first book into several languages.
With the exception of the translations, all of this was material already available online for free from my site. The commercially published books include my name as author and my copyright notice, so although the publishers might possibly object to their being up without my or their authorization, I don't see much reason why I should. Some people may read the books on Scribd instead of on my site, but the only downside of that from my standpoint is that they are less likely to come across other material on my site in the process. And the upside is that some people might find and read the books on Scribd who otherwise wouldn't.
I am unhappy about the first two things I listed, however, because, so far as I can tell, the material copied from this blog contained no link to this blog, and the material copied from the Miscellany did not contain either my or my wife's real names—articles in the Miscellany are given under the names we use in the SCA, since it is about our medieval hobby—or a copyright notice, or any way that a reader could discover that the material was part of a larger book that he might want to look at.
I accordingly emailed Scribd to complain. The response I got was that they could not add anything, such as a credit line or a URL, to material that had been uploaded to their site. I accordingly asked for contact information for the people who uploaded it, and was told that that could only be provided via a subpoena. I have put comments on the text giving the additional information, but I don't know how many people who read the text will bother to look at the comment.
So far as I can tell, the only thing I could do is to file a takedown notice, which I am reluctant to do, and then upload the material to Scribd myself, thus keeping it available, but with the additional information about who the author is and where the rest of it is to be found. I may nor may not bother.