It's funny, but I think that different posters to this thread are talking about different things. One person talks about social widgets for your sidebar, which are like bumpzee, mybloglog, and blogcatalog. Then someone mentioned a "social bookmarking plugin" (that automatically bookmarks your content in social bookmark sites when you publish a post) - like "auto social poster". Last several people mentioned social bookmarking plugin that allow your readers and visitor's to bookmark your site in places like del.icio.us, digg, furl, etc. "Sociable" I've used, as well as the AddThis (addthis.com) service. Personally now I've dumped them both and instead use the "flare" feature that Feedburner provides since you can add all the major services that way - but more importantly because it has a "email to fried" feature that all that plugins like "sociable" don't have.
jtpratt- Can you elaborate on how you get the same functionality using FeedFlares? Do you have one set up for every bookmarking site or just a few?