Screaming Penguin - Source Does Matter

The Ars article on the Bon Echo release notes that its actually a "beta candidate", but still its out there for you to peruse and provide feedback for.

Bon Echo has lots of new stuff under the hood (client side sessions and persistence, more on the client I generally eschew, search suggestions, built in spell checking, SVG, etc).

More info can be found at the devCenter site. (The ars article has the "beta candidate" download links.)