Here's what it does: take any form of media -- DivX/MPEG/whatever video, still images, MP3s, etc -- and load it onto any storage medium -- hard-drive, SD cards, etc -- and this thing will play it back on your TV without requiring a PC. Download the latest Red Vs Blue clips, some machinima, and Battlestar Galactica and put them on an SD card, stick it in your camera and walk over to your friend's place. On the way, shoot a short clip of a street preacher and a photo series at a local garage sale. Take the SD out of your camera and stick it in your friend's Porta-Cinema and bam, you can watch it all, and play any MP3s you've got on your pocket-sized 100GB hard drive as well. The cost of the Porta-Cinema (not including any storage media) was about US$150.
This thing is the bull-goose model of an entire range of similar products. I picked up a no-name 2.5" hard-drive enclosure that has a remote and VGA/composite video/SVHS outputs and plays all the same media formats as the Porta-Cinema (but lacks the flash-memory slots and the clever cartridge system for hard drives), paying about US$70 for it. Another $70 bought me an 80GB Hitachi 5400 RPM 2.5" hard drive. Now I've got a drive the size of an iPod that I can use to play back any video media I lay hands on. (Why the hell doesn't my iPod do this already?)
An oft-repeated mantra about the future of digital media is that no one wants to watch videos on her computer, everyone prefers the wide-screen set in the living room. This is certainly true of some people, at least. These devices solve that problem.
As for me, I'm thinking of going back for another no-name device and loading it with all my family photos and all my parents' photos too, then giving it to my grandmother, who has been feeling excluded by all the digital photography that her brood have been indulging in lately. With this thing, she can watch all the family pics on her TV and take them with her to a friend's house, too.
My friends in Singapore were surprised that I hadn't seen these devices before, but Asia is way ahead of the US, Canada and Europe in this respect. They had one piece of sage advice: spend a little extra for a model with flashable firmware so that you can update the video codecs as new versions of DivX emerge. Good idea.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.