Holy cow - there are more than a couple of pre-built reports, there are 8, which is wonderful! Marketo really needs to update the
Understand The Email Analysis help article to point this out. In fact that help article has a link to the
Built-in Revenue Explorer Reports help article, but it has not been updated with the Email reports.
Also thanks for pointing out the Customize and Display Heat Grids help article - I seem to have overlooked or forgotten most of the RCE enhancements with the June '12 release.