On your desktop/laptop, assume you already have a touchscreen and everything works perfectly. Assume every swipe interaction you have ever used works perfectly.
Interact with the computer. Navigate around the computer. Drag and drop files. Surf around the internet. Click tabs and hyperlinks and whatever with the mouse, with touch, even with tab+space, whatever feels natural.
Do it. Seriously, literally do it. Go through the motions.
My point is simply that once we have touchscreens on every desktop, it might enable ways to interact with your computer that we might not even have thought of yet.
edit: added "similarity to tablet" part
This is what iOS did: Create a new world designed for being touched. Instead of the Windows CE or the Palms around the pointer.
You have to redesign the entire software stack for being touched, and it will happen.
Ubuntu Unity, Windows 8, and Mac OS new versions are races against time for being the first bringing professional creative tools "touch-ready".
It is very hard to do it, and current users are getting angry the same way people got mad when they removed the numeric keys from the macs(so command line software got redesigned around mouse).
I now have an Asus Transformer, and I find that I now reach for the screen on laptops as well. However, when I plug my mouse into my Transformer, it annoys my that I cannot use the mouse as I've comes to expect it to be used; instead, the OS interprets everything the mouse does as gestures.
I hope to someday install Linux on my tablet, and then try to create an interface that treats touch as touch, and mouse as mouse. I also have ideas for touch I'd like to experiment with.
I think the conclusion is rather that soon enough, regular computers will be tablets (or tabletops).
Thanks for all of the great commentary everyone!