please, don't pollute the community or exploit it for PR. Joining Goodreads just for PR is just as bad as when people join AW just to promote their editing or book or whatever, rather than to be an active part of the community.
PRWeb is a press release distribution service and I've used it to promote my books with good results, but you have to be using it to send out newsworthy material and you have to select appropriate media distribution lists. I haven't used Goodreads but from what I know about social networking and book promotion, the advice offered here about how to use it is excellent.
Cheers,
Sandy