First of all, great plugin :).
I went and Googled several of the obscure (to me) social bookmark sites to see if they were worth activating apart from the obvious choices, and found a few that had either changed or simply dropped out of the web. So this is merely a heads-up...
Blue Dot changed its domain to Faves.com. I don't use it, but I thought to mention it since Sociable still links to the old domain.
Also these places seem to be dead or no longer dealing with social bookmarking: