I’ve recently upgraded another computer from Fedora 9 to Fedora 11, and I’ve decided to try the built-in [KVM](http://en.wikipedia.org/wiki/Kernel-based_Virtual_Machine) (i.e. Applications -> System Tools -> [Virtual Machine Manager](http://virt-manager.et.redhat.com/)). I wanted a virtual machine that had bridged mode networking, but it wasn’t available by default. To get it as an option, I disabled SELinux (not sure if it was necessary), followed [some special instructions](http://wiki.libvirt.org/page/Networking#Fedora.2FRHEL_Bridging) to setup a bridged interface, and restarted my network and libvirtd.
Now I’ve got a working guest OS inside of KVM, and I like it. The guest OS feels snappy and responsive.
Update: KVM and the accompanying tools aren’t as mature as VirtualBox or VMWare. E.g. I didn’t see how to get my USB flash drive to be recognized by a KVM guest OS. At one point, I tried to use VirtualBox at the same time as KVM. VirtualBox told me I needed to disable the KVM kernel module before using VirtualBox.