Posts on the Unifiy forums say that the controller doesn't even need to be on for ZHO, the APs manage things once configured.

There is also this:

"People seem to confuse "seamless" roaming with "zero handoff" feature. ZHO is only really needed if you must support sensitive applications that could not survive a normal, or natural handoff, like VOIP for example. That absolutely does not means, that without ZHO you can't have a seamless roaming between APs, it's really the opposite, when walking around, users will hardly notice their devices have reconnected to the network, and are now talking to a different(hopefully near) AP."

Like I said, most people don't need ZHO anyway. And in my experience things like Skype can survive a natural roam between my APs.

Ubiquti have definitely be guilty at times of releasing products before they are 100% ready with the software. At this point the AP code and the controller, even the new version, feel fairly robust to me.