Parallels is great and *almost* a real solution, except for one seemingly small but critical thing - it seems to be unable to recognize a USB printer connected to the mac. My wife uses a multi-function printer for scanning and printing and the inability for Parallels to support WinXP talking to the printer is a show-stopper.
In a different forum a number of people mentioned that they were able to get *printing* to work using an Apple-supplid program called Bonjour. This seems to work for people using Airport and a network shared printer but this isn't an option for multi-function USB printers without losing some functionality.
Parallels also has a limitation of 2 USB connections. My keyboard/mouse take up two USB slots so that may be part of the problem, but even with the keyboard removed temporarily I was not able to recognize the printer.
So, my overall conclusion is "great concept, almost there" but unless you're willing to sacrifice some functionality it's not ready for the mainstream user.