If I had to guess I'd say that adding Leopard and Vista support has contributed to Parallels' increasing size. But it is easy to use, for the most part. The most challenging thing for me has been getting used to the differences between Parallels Desktop and Virtual PC.

Among the things it does well are the easy install - start it running and walk away for awhile - but not too long; Windows XP installs relatively quickly on Intel Macs. It's ability to utilize a Boot Camp version of Windows is also very useful. And XP runs well in Parallels.

The biggest problem I had is with their documentation. Just figuring out how to set up printers required me to jump all over the place: a piece of info here, a piece there, etc. Fortunately, Adobe Reader 8 has good find capability or I might never have sorted it out. It's not so hard once you get the hang of it, but unlike Virtual PC you do need to install appropriate printer drivers in Windows. And using a printer in Parallels/Windows disables it in OS X. Fortunately it's easy, once you know how, to turn USB access to particular devices on and off.