I was actually just formulating a Demo post myself!
I would love to have a demo. In the world of Demos the two best I have seen are the original Doom and the original Mount & Blade. Doom gave you 1/3 of the game for free, encouraged you to share with your friends and had the "How to Order the Full Game" info display once you beat the final level. Mount & Blade gave you full access to the entire game but capped your level at 7, if you like the game you can buy an activation code and keep using your save games with your demo character.
Here is something else to think about. Demo's are for convincing people to buy the game by giving them something to try out.
Is anyone here not going to buy the game anyway?
Demos also give you a good idea of how well the game will play with your PC. Since Skyrim is using a brand new engine there are a lot of technical details that could cause problems, I would prefer that the developers are aware of those problems before the initial release.
I think there could be a demo that completley disables the Console and Mod Support and puts the notoriuos
invisible walls about 1-2 cells away from the initial city/town where the game starts. There would not even be a need to include textures and models for things outside that area in the demo BSA.