I think this is going to be one of those threads like the iPod thread where everybody is calling it "useless", "just a gimmick", "will be dead in just a few years"...
Multi Touch is the future of UI. People are trying to apply multi-touch to the technology and standards of today... which is why it doesn't make sense.
PC's as they exist today will be seen as relics of the past.. sitting at a desk or with a computer in your lap for hours doing all your work and entertainment? Why?
"Computers" will be decentralized, casual use and specific use devices –ubiquitous to our daily lives.
You'll be able to go up to a wall or a screen on your fridge and quickly pay a bill, manage the home HVAC or purchase a song to listen to while you make dinner.
If you want to sit down and watch a TV show or view your photos, something like

TV will be the device you turn to.
You want to read the news or certain writing based website? Grab a tablet that looks like an oversized iPhone, hit a few touch screen buttons to go to your favorite site and begin reading. Drag or flick to scroll/change the page.
I can see multi touch becoming very useful.. just not with the standard setup we use today.
I've been saying it since Leopard was launched: Leopard is the last OS X iteration. I'm willing to bet that Jobs will announce the next version of Mac OS will be a multi touch based OS that will move in the direction that I've explained above.