I'm very flattered with David Chartier's compliment. Not being able to move the Mail.app's sidebar was indeed also one of my gripes, although introducing the sidebar as a replacement of the drawer was a great move by Apple. I enjoyed implementing the sidebar in ecto, it looks cleaner than a drawer.
There's more to ecto's sidebar, by the way: Control-click in the blue area next to the resize button and you can change the background color. Not as exciting, but some users might like being able to see something else than light blue.