If you've ever used a wiki, it is pretty much the same principle. For example, headers are just underlined words. And bulleted lists can be created by simply using a bunch of asterisks. Like zis:
Title
=====
* item 1
* item 2
* item 3
What makes Markdown powerful is that the syntax is decoupled from a specific web service (such as a wiki). This means that you can write your docs in your favorite text editor (insert obligatory emacs vs. vi showdown reference), and convert it to HTML with a single command. The standardized format means you have very elegant looking README text files, that easily turn into first class html pages once passed through the Markdown converter.
There seems to be a whole eco-system that has evolved around Markdown, and it appears to be the format of choice for a number of git based code repositories. Now if only Blogger supported the Markdown syntax.
And once again, I've jumped on the bandwagon much later than I should have.
