I discovered LibraryThing about two months ago and immediately signed up for their service. I've always wanted to catalog my library and LibraryThing made it easy. Now my readers can see what I've got in my library. (Mom, Sis, this doesn't mean you can raid my library indiscriminately, although I'm willing to swap book hostages.)
I purchased the Cuecat scanner from LibraryThing, and entered 80% of my books in just three days of effort. Now I just need to enter the difficult books - those lacking ISBNs and Library of Congress numbers, or with odd publishers. (This includes several bibles.)
Also, I've been scanning in book covers when I have time. LibraryThing is excellent at locating book covers if they exist - but even so, many of my book entries are missing a cover graphic.
It is fun to browse the books in other people's libraries, and to see how their library contents match up with mine. (Good matches are potential friends!) Some people have amazingly large libraries - 5,000 books are not uncommon! I'll probably have a thousand books cataloged by the end of the year, but I'm just chopped liver compared to some.