I'm finding that StumbleUpon has been the most effective social button on the site. I've been consistently sharing my blog entires on StumbleUpon and other content sharing sites like Digg, Reddit, Twitter, Linkedin, +1, Facebook, and maybe a couple other ones. It's mostly a waste of time except for StumbleUpon.
Senh: In terms of analysis, the article is similar to what I wrote. Mainly, Facebook, Twitter, and Yahoo Buzz got into link sharing and pretty much pushed Digg aside. Digg execs attributed the lost in traffic to Google's new algorithm which resulted in less referral traffic to Digg. The article also has an in-depth write-up of its history.
The latest version of Digg - aka Digg v4 - is getting a lot of negative feedback from its users, especially the power users. They’ve lead a Digg Revolt by pushing articles from their rival, Reddit, to Digg’s homepage. Now, they’ve defaced the site’s comment system by littering it with anti-Digg comments.