Touchscreens are ideal for casual use, content consumption devices, but insane for prolonged productivity (ie; business).
Strangely, I think Microsoft is either ignoring, or simply not far enough along in development for using improved webcams for gesture-based interface improvements, a la Kinect. But dragging your fingers all over your desktop screen for 8 hours at a time at work is ... just no.
A big barrier is the tens of trillions of hours the collective business world has already invested in getting people to be productive and efficient with using a keyboard and mouse and familiar interfaces for interaction and production.
Sit down typical person in cubicle. Give them Windows 7 + Office + Acrobat. Tell them type this document, use these sources, make a PDF with fields, and then make a spreadsheet with some of that data. It's not too hard to get this done. Take same person, give them Windows 8 + touchscreen, and watch how if anything, efficiency plummets. Metro is the enemy of simple multitasking and efficiency for business use.
For mobile devices, I don't see that much of an issue. It's relatively hard, even with a BT keyboard, to get serious work done on an iPad or Nexus tablet in the same efficient manner as a desktop user with kb/mouse/typical 20-22" widescreen. You can't honestly compare the experience of being able to easily open and switch between dozens of apps/tabs/docs quickly in an efficient manner, and having full-screen apps/interface slowing your progress.