[Ogre]

Glitchiness of occlusion may be driver or hardware dependent. I've been using it successfully, but haven't tested on a variety of hardware. The bigger issue is the two way communication between GPU and CPU. You want your pipeline to be one way, otherwise you either have stalls waiting for results (poor or inconsistent framerates), or things becoming visible one or more frames later than they should. For some applications, the latter is acceptable. For Minecraft (style) chunks, it might mean sometimes large amounts of terrain popping in a frame or two too late, which could be very noticeable.

It seems like a combination of both might be feasible. Do something smart like this article on the CPU, which feeds into a greatly reduced set of occlusion queries, small enough to perhaps not introduce significant stalls using the first method.

However, in this article's case, he's specifically targeting the mobile edition of minecraft, where hardware occlusion is not yet universally available! So fast CPU versions are definitely warranted, and I think he's got a really good solution.