If the proof is in the pudding, well, it looks like we've got the pudding—or a video of it, at least. A paying customer of Psystar, the controversial company that’s selling Mac OS X-compatible PCs, just got his Open Computer, and he's posted a video of the machine in action.

Gizmodo got its hands on the video, shot by a reader named Patrick, which shows him running a video cable from the $399 Open Computer to an LCD monitor. Patrick then hits the blue power button on the front of the box, and after about 45 seconds of Windows-looking text flashing on the screen, the Mac OS X "Leopard" desktop appears.

Patrick tells Gizmodo that the Open Computer runs "pretty damn fast"—however, Apple's Software Update utility doesn’t seem to be working properly, so the system won't be able to update itself automatically. In its FAQ, Psystar has warned users against installing "untested" OS updates from Apple—a pretty serious drawback to the clones, although I'm sure enterprising users will find ways around that limitation.

Meanwhile, Psystar posted a video last week showing three Open Computers in action: one running Mac OS X, the Linux-based Ubuntu, and Windows XP.

So, after all the questions about Psystar's legitimacy, it's starting to look like the company's Open Computer is the real deal. Now, of course, the question is how Apple will respond to this apparent violation of its Mac OS X user license; so far, not a peep from Cupertino about Psystar.

Anyway, what do you think—are the new videos convincing? Anyone ready to plunk down $400 for an Open Computer?

Related:
Exclusive Video: Psystar in the Wild [Gizmodo]