Parallels just released a new patch to their software which lets me run Windows Vista and Mac OS X simultaneously. I highly recommend that everybody using Parallels 3 Update to Parallels Build 4560 sooner rather than later.
In the previous build of Parallels (4128) - Windows Vista would suck up 70-107% of my Mac's CPU even when Vista was idle! (I think CPU usage can go over 100% because I have a dual-core Core Duo 2 machine).
But now with Parallels Build 4560 - Vista still sucks - but it sucks less...only 24-47% now. And that is good enough to leave Windows running full-time on OS X with Vista in Parallels.
The image above is my MacBookPro connected to a second monitor. The MBP's laptop screen is running OS X full-screen, and the second monitor is running Windows Vista full-screen. Today - I'm 200% more productive thanks to that Parallels patch.