That's pretty cool. This is truly lightyears better than the older versions of Sheepshaver that I have used: it is fast, it feels polished and it appears to be reasonably stable. There are, however, four minor irritations: first, it won't work on a PowerPC-based Mac in its entirety. I found, however, that if I poked around inside the application, I could run Sheepshaver without the wrapper app following traditional setup procedures (if you look inside, it will make sense). It feels about as fast on a Core Duo MacBook as my 1 GHz Titanium PowerBook does natively in OS 9 for my brief testing. That is about right, actually. As I understand Rosetta and similar emulators, if two cores are available, it will use one each to translate and execute instructions, meaning two things: it runs at about 1:4 speed compared to native code (i.e. a dual 2 GHz processor is roughly equivalent to a single emulated 1 GHz processor) and uses about 140% of the CPU in the process, my second complaint. Portable owners beware.
Third, I couldn't get full screen to work. It would hang at a gray screen until I force quit it. By extension thereof, the default screen size is 1024x855. The MacBook this was tested on only has a 1280x800 display. For that matter, my Titanium has a 1280x854 display, one pixel shorter than the default. To change the setting, you need to find the prefs buried in the app and edit them by hand. I can't imagine how bad it will be for anybody with an 11" MacBook Air ("Why is the window twice the size of my screen?").
All this said, it seems to work very well. It thinks it has a video card equal to the amount of system RAM you have free (on my Titanium, this is typically about 650 MB). Assuming that there is a reasonable amount of hardware graphics acceleration, I don't see why it couldn't run OS 9 and Ares well. I didn't even have to tweak the extensions first. Very little setup required. A very nice find.
Oh, and for whatever it is worth, Chubby Bunny comes with a handful of productivity apps including MORE and WordPerfect to sweeten the deal.