reading thru library thing blog - excellent:

Next up, more social features, including library-to-library matching ("whose library is most like mine?") and the ability to, when browsing someone else's library, add the book to your collection.
Profiles now show users with overlapping libraries, so you can spot who has similar tastes.
When you look at someone else's profile you can now see exactly what your "shared" books are.
When you browse someone's library you can click on [+] to add a book to your collection.

Well, I think I've come up with the right solution, using Amazon and the LC together. It's a little complicated, but the complexity is hidden from the user. It works something like this. First it looks in the LC. If it can't find it there—either because it's not there or because the search didn't follow LC rules—it goes to Amazon. If it finds it on Amazon, it makes one last heroic and generally successful effort to find it at the LC, this time using Amazon's data in a LC lookup.
When there's LC data, it tends to prefer it over Amazon data. This is because Amazon plays a bit loose with authors and titles.
Inevitably the multiple sources hamper attempts to "match up" equivalent books. Right now it tends to match books up by LC control number (which can embrace two ISBNs) or by ISBN. In the future I'll be doing a more sophisticated sameness test, involving titles, authors and other data. The same/different issue can never be solved fully, but I'll try to strike a reasonable balance.
I've added support for Amazon.co.uk, Amazon.ca, Amazon.fr and Amazon.de. mmmmm.

You can now leave a comment on someone's profile page (eg., "hey, I have lots of books on Maori art too!"). You can shut off comments on your profile page. By default I shut it off on everyone with a private library (about 20 of 680).

Comments suggest that $10 isn't a big barrier for people. I may raise this a little in the future, or switch to a yearly rate, but "free or cheap" will always be the deal, and, of course, current paid members are locked in for life.

By popular request, I have tentatively installed "autocompleting" tags on the Add Books screen (click "autocomplete tags.") Autocompleting means that when you type part of a tag, LibraryThing will suggest the rest of it based on previous tags. ok. -I'd still like to see all my tags while adding ...?

How interested are people in reviews? Should I, for example, have a "Reviews" tab like the "Tags" tab? Would this convey the impression that LibraryThing was all about reviewing and discussing? I want to keep some focus. This site is not a universal book portal. It's a book-cataloging service with some diverting social extensions. good.