I always post a link to new Hubs on my Facebook profile, as well as on the "walls" of some friends and groups I belong to there.
I mainly write about music and movies so I'm also a member of numerous forums devoted to those subjects. When I publish a new Hub on either topic I'll post the links there as well. (I should point out that I am also long time active member at most of said forums, and don't just drop in simply to post links -- if you do that, forum communities generally will treat you like a spammer and ignore you.)
I've tried linking at Digg and Reddit and gotten next to no response from them so I don't even bother with them anymore. There's so much going on at those sites that unless you're lucky enough to start the next viral sensation, you get lost in the shuffle very quickly.
I started a Linkedin profile when I was job hunting a while ago and used to put the links there too, but I rarely, if ever, use Linkedin anymore. I never got many "bites" on my Hubs from there anyway.