There is recent discussion from Sean "Early" Campbell regarding the Gateway version of this product category.
This is a gadget that I'm trying to get sooner than later. When I described it to my wife, she even had an interest and gave a tentative 'go ahead' to the purchase.
In short, these things are a component for the entertainment system that will hook to your wired or wireless network. They are then able to access media collections (MP3, WMA, JPG, MPEG, etc.) from one or more PCs on the network. What formats are played depends on the particular device.
I've looked at more than half a dozen versions from Gateway, SMC, Creative Labs, HP, Prismiq, Linksys, and others. So far, I eliminated the Linksys and HP options for various reasons. The Gateway is still in the running, but the Prismiq seems to have the most going for it. I am hoping to see it in person to check out its features. Gateway is the only one that I've been able to see demoed (at the Gateway store, of course).
As easy as it is to get content onto the computer now and the likelihood that more will be there due to online music ordering, a device like this just makes sense. I'm not too concerned with the ability to play video, though; I figure that by the time I have a substantial amount of interesting video on my PC, there will be newer and better versions of these products on the market.
We'll have to see what Santa has in store this year!