Yes, to me they always looked like a strictly value subtracting service in terms of functionality, making the documents they host less convenient to read than they were in their original form.
I don't know why, but I've determined that Scribd is evil where Amazon is not. This is an intuitive conclusion based on lots of observation. I think that intuition is based on the fact that Amazon made DRM on Kindle to satisfy their publishing customers so those customers were more willing to distribute to a wider audience where Scribd made DRM to empower themselves and restrict distribution of re-appropriated content. Also, mandatory Facebook integration..
Yeah, ditto. The attempts to "go social" and monetize felt sleazy.
Guess what, when I'm googling for some PDF or I find some guy's slides, I don't want to tell my friends, and I don't want to "buy the article" for $14.99 or whatever like it's frickin' JSTOR.