If you create an Image of Win 7 before starting the Win 8 Installation, then reverting to Win 7 is easy. It takes about 10 minutes to restore from an Image.
I use Acronis True Image 2013 and can easily revert to an earlier OS.
Legally if you remove the Win 8 installation you can then start using the Win 7 OS again. But you can then not use Win 8 unless you replace a different qualifying OS.
With some customizations you can use Win 8 very similarly to Win 7 with some added benefits that come with Win 8. I have added a tutorial
here that will go a long ways toward making Win 8 feel more familiar.