This is one of several new features recently added to WordPress.com. Here’s why it’s good. Now people can send you an email without you ever publicly displaying your email address.
My first thought was that it might be even more useful in the sidebar than in posts or pages. A response to that is that, once the contact form is in a post or a page, you can link to it from the sidebar. I might just do that.
Anyway, here’s the contact form. Whatever you type in here will be emailed to me.