Okay, I lied. KQEMU is not the only open-source virtualization solution. VirtualBox is another, and is partially GPLed. Features that are attractive to corporate consumers (iSCSI and USB support, among others) are available only in their proprietary product, but the rest (including the required kernel module) are released on their public Subversion server under the GPL.
I compiled and messed with it last night. The performance is amazing. By amazing, I mean that it boots Windows XP faster than VMWare... and faster than it boots natively on my computer. There are "additions" that are comparable to VMWare Tools, such as a graphics driver and a mouse driver that enable tighter integration with the host interface.
It did crash several times last night while running Windows XP. Today I recompiled it after updating from Subversion and have not seen any crashes yet, so I'm not sure if whatever it was got fixed. There are still some bugs with snapshots that cause the VirtualBox server to crash, but so far they haven't damaged any of my virtual machines.
After all considerations, I'm ready to ditch VMWare. Open-source virtualization is finally here, and it kicks butt.