I wanted to include a feed from my Google Books page here, but it didn't quite work out as I had wanted it to. I'm using Google Books as a way to keep track of some of the texts that I have read, am reading or aspire to read. I have found that it is a reasonably good place from which to scan contents pages, especially if it is a book that I need to order or buy. I've also been tagging things that I've lodged there, just because I can.
Google Books isn't the main keeper of my bibliographic info, however. For that, I use Zotero (v 1.0.10). I have found it to be the best way to keep a bibliography. It allows you to tag, make groups from your library, and most usefully of all, keeps screen-shots and files linked in with each reference. There is also a plug-in to Word, so that it automatically inserts references in the style you need, and creates a bibliography for you. I think it is a really powerful tool, and a very reassuring PhD ally. I don't yet use the online version 2.0 (beta), but I will once its stability can be assured. Also, I think someone has made a WordPress widget for it...so my bibliography might one day appear here.
(Thanks to Pete for mentioning delicious too (comment in post below) - I have tried it and really like it, but end up going back to Zotero, just cos I wanted everything in one place and am too lazy to keep both of them simultaneously neat.)
PS. I am currently reading George Yudice's The Expediency of Culture and Paul Morand's Venices. Guess which one is on my bedside table?