I can envision them being useful for specific types of applications, as long as a very expressive and intuitive gesture system is in place. Along the lines of the ipod, but far more sophisticated. I think applications would need to be almost entirely touch based to work, regularly switching input types would be disruptive. And I don't think it will go anywhere on desktops.

I was recently checking out some of the new HP home computers with touch and my first thought was cool. After a minute it changed to cool, but pointless. If you're using a desktop it's awkward at best to leave the keyboard and mouse to touch the screen. And then the screen is greater than an arms length away. So you probably won't unless there's a feature that you HAVE to use touch for, at which point you'll just be annoyed.