From the everyone probably already knows this dept . . .
I had hesitated to make the Sheepshaver-WordPerfect Install full screen (as default -- it's easy enough to change) because of issues switching from SS to other applications. With the SS window smaller, you can just click outside of it to go to OSX, but the window's still there. You'd need to minimize the SS desktop, one more click, or various utilities or the dock menu can hide windows of one app for you when you switch to another.
Then I poked around Spaces, the window utility that comes with OS 10.5 and later, and found something that's almost too much fun.
Assume you've been using your Mac as usual, with various open application windows in Space 1. Switch to Space 2, close any application windows in that Space, and start Sheepshaver. Don't have open windows in Spaces 3 and 4. Now, using command-tab will switch directly between the OSX desktop and SS desktop.
Remember Andy Hertzfeld's legendary Switcher, circa 1985? It had the Berkeley Mac Users' Group jumping for joy. And this is just like it! I'm very happy with this.
It's apparently even better in Lion, in which Spaces and Expose have been merged into Mission Control. It gives you the option of handling full-screen windows differently.