As far as I'm concerned, Library Thing opened up a whole new world for me. One day I was a solitary reader sitting at my computer when I saw it mentioned and thought I would take a look; half an hour later I had a lifetime account and was pulling books off shelves, banging the dust off them and discovering that half of them predated ISBN numbers. Nonetheless I have catalogued that 760-books that are on the shelves in my room and the hallway (haven't finished the hallway yet). Then there are the books in our upstairs living room - hundreds more. But I've already found books I'd forgotten I had (so many of the shelves are double-stacked) and I can spend happy hours checking I've got the right book jacket showing, or adding information to share with other users. I'm fairly meticulous about adding books as I buy them but, unlike some people, I only include books I actually own.
If not an online catalog, do you use any other method to catalog your book collection? Excel spreadsheets, index cards, a notebook, anything?
The most important change for me was that it was through Library Thing that I ventured into a world of like-minded people, at first through the groups on Library Thing itself, which are many and varied. However, following a link on another reader's profile one day led to the discovery that there were more sites devoted to talking about books! Once I started reading other people's blogs it didn't take long to decide that I would enjoy doing it too, although I didn't expect anyone but me to read what I wrote. I use my other blog to keep a monthly record of all the books I've read, now (though I haven't quite decided whether this is the most convenient way of recording this information) and try to review as many as possible. Over Christmas I shall update my Library Thing links to reviews and do some more cataloguing. The family may laugh, but I'm pretty sure my elder son keeps a music catalogue.