I am looking to use this feature for two purposes: scanning books (one camera pointed at each of a pair of pages), and for stereo 3D photography.
I would like to be able to preview and capture photos from two cameras simultaneously, and download them to my Mac (recent laptop, Mac OS X 10.8.x). Being able to keep track of which photos were from which camera is also a must.
I see a couple of packages that will do this via USB tethering on Windows, namely PSRemote Multi-Camera (which other than being on Windows, looks perfect for my needs) and StereoData Maker. I certainly could run Windows on my Mac somehow, but I'd rather avoid that, if possible.
I haven't bought the cameras yet, and I do not have any requirements as to which cameras are supported (it seems the packages above only support Canons), other than that they be relatively inexpensive. This is a hobby-type project, not a $3000 dSLR-type project.
However, even if all you have is a dSLR solution for this problem, I'd still like to hear about it. Perhaps it will lead to related solution.
Inventive hacky solutions welcome!