LibraryThing is becoming widely used online, however has limitations on the number of book entries you can make before you have to start paying, and I’ve also found the software to be full of glitches. GoodReads is a similar thing which has been recommended to me. It is totally free with no limitations of book numbers, and you can also set up different shelves (e.g. a “To read” shelf which is essential for me!). I’ll be giving it a go to see if it’s preferable to LibraryThing, although the WAP site for LibraryThing is great when you’re out and about and can’t remember the name of that book you’re after or aren’t sure if you’ve read something before, and I’m not sure if GoodReads has this.