I have been working with Sava for the past month or so, and have been very impressed. It seems like a very solid, full-featured product, and the new plug-in architecture makes integrating external code a breeze. I was tasked with taking a fairly large legacy Fusebox application (it's been incrementally developed for the past six years or so) and finding a way to use most of its features from within Sava.
With a bit of help and support from Matt Levine, I was able to use the new plug-in architecture to accomplish that feat, without having to touch any of the existing CMS code. Now that's extensibility!
I plan to write more in the future about what I've been doing with Sava, with a particular focus on integrating existing code with it. If you're looking for a ColdFusion CMS I highly recommend checking it out.