I do. I will mix down my project to a stereo wav file, then I will open a new project called "(whatever the name of the song is) master". I use a waves mastering suite (expensive, but nice) and follow a few guidelines I've picked up over the years.
I'm sure what I do woudn't be considered "mastering" by people who really know what they are doing, but to my ears it sounds way more "radio-ready" than the original mixdown.
Here is a little mastering tutorial that uses some of the waves plugs that I've got. I've had some good results using these guidelines in cubase.