Lulu.com is a self-publishing site for hardcopy publishing -- you upload your ms and cover and such, and you can put your book up for sale. It's not really a networking tool, per se, but it works well as a distribution tool for me. I'm an avid reader, but the issues that apply to selfpub in general apply to Smashwords -- there's just no gatekeeping, so it's possible to waste a lot of time on bad books.

Are you looking to use Twitter to publicise or network? It can be useful for both, though I've found it pretty constricting.