A huge challenge for writers, whether traditionally or self published, is spreading the word about your books. Some people spend thousands of dollars hiring a publicist, but how do you know if you will get your money's worth? And if you are working on your own, how do you know you'll get your time's worth?
I have been somewhat active on Good Reads. I also have profiles on Library Thing, Jacket Flap, Red Room, and Authors Den. It takes a few hours to update all these sites every time I have a new book out, but it's important to have your book where people can find it.
Another community of book lovers and reviewers I've discovered recently is Ask David. Although not the largest out there, it offers a free opportunity for authors to promote their books, including a free book promotion page, links to websites/Facebook/Twitter etc., and the potential for reviews from users. It only took a few minutes to fill out the form, and they do the rest. This service can be free to the authors because the site gets a small commission from Amazon for sales through site links.
As authors, of course we'd rather spend our time writing – but it's worth trying some of the promotional sites, especially the free ones.