Since last Feb 2007, I have been running Windows XP Pro SP2 on my MacBook Pro 15" using Parallels. It's true that Parallels had some issues early on, but I still found it to be reliable than my several Dell laptops and workstation.
In March 07, I received my MacPro 8-Core. I run WinXP on this machine too using Parallels. 95% of my use on the MacPro is for Mac programs like Lightroom, iWorks, iLife, Mac Office and Photoshop.
However, on my MacBook Pro, I use it for my financial planning business where Windows is running 8 hours a day in order to run ACT! 2008 Premium (CRM), MS Office 2007 and Internet Explorer 6 for financial web sites that can only be accessed using IE. I have an external 27" LCD wide monitor so that I usually have the external monitor for Windows and the laptop display for Mac OS pgms.
All of the unit work very well even after the Leopard upgrades. I have to use Windows pgms, but I will never go back to using a PC. The latest version of Parallels runs great. I highly recommend it.
North Wales, PA