Amazon (NSDQ: AMZN) is buying up another books-focused social network Shelfari, three weeks after it acquired AbeBooks, which holds a 40 percent stake in Shelfari’s main rival, LibraryThing. The Seattle-based startup was founded last year by Josh Hug, the former director of device engineering at RealNetworks (NSDQ: RNWK), and in fact Amazon was a seed investor in the company…it had raised a total of $1 million.

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Interestingly, there is no love lost between the two rivals Shelfari and LibraryThing, as SeattlePI describes: LibraryThing founder Tim Spalding has called Shelfari a “bad actor” for engaging in what he called a massive campaign of “astroturfing,” the practice of planting positive comments about a service on blogs. It is likely that AMZN disposes of its stake in LibraryThing, or could conceivably be merged together.