When your readers are on your blog's home page, they can click "Share" to post the blog's URL to Twitter, Facebook, or Google Reader. If they navigate directly to an individual blog post, clicking "Share" in the navbar also lets them share the post by email.
We've already seen some nice adoption of this new feature and hope this helps you build out your audience and share your story with the world. Here's a fun hack: each URL that gets shared has a specific parameter appended (?spref=nn, where fb=Facebook, tw=Twitter, and gr=Google Reader). If you're using Google Analytics to measure traffic on your blog, you can search for those strings to see how much traffic you're getting from each source.
On the other hand, if you're interested in seeing which blogs people are sharing, head on over to Twitter search and you can watch as people share blogs and posts that they like. Don't forget to follow us on Twitter while you're there!
This is one of many features announced as part of Blogger's 10th birthday. Happy Birthday!