From an end-user's perspective, the main difference with Delicious Library is that it looks like you're going to make me type in my book's details. The ease of

From an end-user's perspective, the main difference with Delicious Library is that it looks like you're going to make me type in my book's details. The ease of entering data into Delicious Library is much more valuable to me (and a lot of people, I think) than the 'always available' nature of an online service (which has its drawbacks: you go bust and my data goes with you) and the 'show off' factor from your social/sharing platform. As well as scanning ISBN barcodes, I'd also look into importing data from existing applications (like Delicious Library) or as CSV/similar files. The early adopter of your service is probably someone who already has some form of cataloguing going on already - take advantage of that and don't ask your users to do a ton of work they've already done somewhere else. Good luck!