Ask HN: Is PLR/MRR/RR "rebranded" marketing content bad for UGC sites?

So I've never been a fan of affiliate marketers, and I'd heard about "private label rights" (PLR) and "master resell rights" books before, but lately I've noticed these things seem to be everywhere. They're all over docstoc, scribd, and issuu. I've even seen people sell them on ebay.

Examples: http://www.docstoc.com/docs/5836713/How-To-Be-A-Successful-Forex-Trader http://www.docstoc.com/docs/7236710/Newbies-Guide-To-Resale-Rights

Anyway, I can't imagine these are good for sites made from UGC. I mean, this stuff is basically spam. Does anyone have any experience with this? Like, do they significantly drag down user experience? Does Google penalize this stuff? Is it actually effective marketing?