[Ulzgoroth]

Have you read Neptune's Brood by Charles Stross? I bring it up because it is a book with pretty hard science, plentiful nanofabricators...and space pirates.

While getting into all their schemes would be telling a bit too much, their major interests in boarding ships appear to be inspecting them and their cargoes, partly for insurance reasons (they are technically an insurance agency branch office) and partly so that they can engage in commodity futures trading using inside information about any cargo that hasn't been publicly disclosed. (Actually physically stealing bulk cargos would be a waste.)