To run desktop apps, you can go to the desktop. I've been using it as my primary OS for several months now

Disclosure: MSFT Employee

I recently bought a laptop and it's the first time I've had windows on my home machine since 2004. Since it's only $15 to upgrade: Is it possible/easy to upgrade and go back to Windows 7 if I find it detestable?

Going back means using the restore disks or partitions that came with your computer, or installing fresh from a retail DVD of a previous OS. There's no "downgrade" process.

Of course, 1% of your time is spent in Metro if you use it on a desktop, and that's generally when you're searching for something.