I am impressed.
Installation was simple, and it has all the functionality of Trixbox, and then some. Like Trixbox, it uses FreePBX for the actual management of the PBX, but unlike Trixbox, it runs on CentOS 5, and lacks the annoying "feature" of having all Zap functionality die if you happen to be running on a non-multicore CPU.
There are a host of modules already available, including some nifty text-to speech features, but I haven't had an opportunity to test those as of yet. I plan on doing so next week, just to see how things work.
One added bonus -- for some reason, PBX-in-a-Flash actually fixed one annoying problem I had with Trixbox: on my outbound trunk using Vonage, I often had problems with IVRs (when I was dialing the phone company to complain about another billing error, for example). The whole "press one for sales, two for tech support" etc. didn't work a lot of the time. Now it does.
That alone was worth making the switch.