It's true. OQO is the smallest UMPC available. Oh and did I mention it also addresses my complaints about fitting in your pocket and having a keyboard? The OQO is indeed a great idea. The only two things holding it back right now (which I also have issue with on the Origami-style devices) is price and horsepower. I don't really know much about how the battery performs on it but I think decent battery life is unrealistic with today's technology on a pocket-sized x86 device.
So anyway, if OQO can somehow get the price down, I think it'd be a pretty awesome PDA replacement.
(Update: Sorry I should have been more clear. I am fully aware that the OQO isn't Microsoft's definition of a UMPC but it fits my definition and the English language's definition so I am boycotting the UMPC term because it's too exclusive. I'll call any hand-sized PC a UMPC and I'll call the MS defined ones Origami.)