Starting with version 2.6, Movable Type offers a new feature that allows the blog author to easily set up something called a Creative Commons license for their blog.
Under copyright law, you as an author hold the copyright for anything that you've written, as soon as you write it. This prevents others from distributing copies of your work without your permission except for certain exemptions like fair use. The Creative Commons License is a license that you grant to others allowing them to copy your work under terms that you set. There are a number of licenses available (eleven to be exact), each of which grants different rights.
I found an excellent analysis of the legal issues involved in putting a Creative Commons license sticker on your blog. I strongly urge everybody to read this if they're interested in making their writings available under one of the Creative Commons licenses. There are some ambiguous provisions in these licenses that may have unintended consequences if you grant a license and then decide to revoke it.
Added 3/13: An updated version of the legal analysis is now available.