Not too impressed so far. It's a plugin that links your site to wordpress.com and some of its services. You have to have a wordpress.com account to start, which is no big deal.
It's a compendium of several older plugins like After the Deadline and WP Site Stats. You can see the screen shot here:
http://awesomescreenshot.com/0c68xf2bc
Looks like there will be additional pieces coming.
The Sharedaddy part is underwhelming. I tried the email sharing icon. It produces just an email field to fill in, no ability to use your Gmail contacts.
Meh.....