Parallels release yesterday of a new beta (build 3094) further blurs the distinction between rival operating systems. With the new release, Windows applications appear independently in the Mac OS X dock, and even in the application switcher. Better still, Windows XP apps can be dragged to a permanent spot on the dock, and when clicked, will launch Parallels, boot Windows XP, and then launch the application. My experience has been that Windows XP boots way faster on my iMac Core Duo than on my 3.0 GHz P4, so this delay is negligible.
Below are screenshots, the first showing individual Windows XP applications in the dock, and the second showing a Application Switcher screenshot.