Channel 9 have posted a great video of the new Portable Media Center's. The video is an overview of the devices from Brett Bentsen (Product Unit Manager of PMCs).
Portable Media Centers allow you to have all of your favorite video, music, and pictures wherever you are. At WinHEC earlier this year, I personally demo'd the Creative Zen Portable Media Center and it was rather impressive. The ability to store all your entertainment on a device that has a good battery life (8 hours) and one that can output films/TV recordings onto a TV is the unique selling point of the PMCs. PMCs are likely to be a huge hit with kids and teens wanting to watch their favourite TV shows whilst travelling.
If you're still not sure what the PMC is or are interested in the devices then check out this great overview below!