According to Gartner by 2008 at least 10% of employers will require laptops to be provided by employees. All I can say is I certainly hope so. I’ve used my personal laptops for at least three employers in the last 6 years.
I’d much prefer to use my more productive Mac laptops versus your generic IT provided Dell laptop. The unwritten conclusion I can make is though they’ll require an X86 laptop running some specific version of Windows. Unless things like AlienWare and Apple laptops show up in some laptop magic quadrant.