Sometimes people have misconceived notions about virtualization performance, typically based on experience with old-school software-based chip emulation of the sort that Virtual PC for Mac provided on the PowerPC platform. These past experiences lead them to think that high performance applications like Naturally Speaking will have issues running under VMware Fusion, like they experienced with Virtual PC for Mac.
Well, VMware Fusion actually "virtualizes" the Intel processor on the Mac, allowing the Windows OS, and the applications running on that OS, near native access to the physical CPU.
This is the big difference between "emulation" of the sort provided by Virtual PC for Mac, and the "virtualization" provided by VMware Fusion, and the performance difference is huge.
Some people mix them up in their thinking and it's our job, and the job of our smart users to help clear the air, mostly so people realize that they can indeed have access to all the great Windows apps they want, right there on their Macs.
One VMware Fusion user in Italy is doing just that. He's posted this neat video of him using VMware Fusion to run Windows on a Mac so he can use Dragon Naturally Speaking to take dictation. The speech recognition is even in Italian! Very cool!