If you want a little computer that is extremely mobile and can follow you to the meeting table or the bed then a slate device is where it's at. The technology simply wasn't there before. Most of the old tablets only worked with a stylus, the ones that had touch screens only had single-touch and were very poor at detecting them. Now we have multi-touch capacitive and much smarter software and more powerful hardware. The iPad still sucks because it is an overgrown iPhone, a novelty that keeps you locked into the app store. Windows slates will be useful. And before the mac fanboys start flaming me over "But windowz isnt design for touch", Windows 7 works very well for touch. Also, since it can run any windows software there will be more software specifically designed to help touch screen users.
Personally, I will be getting a new generation slate PC, probably the HP Slate or the Hanvon BC10C.