After a lot of changes, I use a simple spreadsheet (the way I began cataloguing my books the other century, after all) AND goodreads for what I'm reading at the moment (see signature). Don't plan to make it my primary database for books, though.
I
could do with Delicious Library, but I have far too many Italian books (and the ones form the 1970s-1980s don't have the ISBN, so) and the interface isn't that terrible (plus throwing together dvds, vhs, tapes, cds and books, yuck). And it's quite costly too- after all, the only nice/geek-fascinating feature is the barcode reading, so, uhm, I can spare those dollars to buy more books
