[Parallels](http://www.parallels.com/) rocks. It is the first virtualization software for the Intel Macs. They also Windows and Linux but they aren’t well known compared to the big guys of Microsoft Virtual PC and VMware. The performance is pretty good since it makes use of the Intel VT extensions in the Core Duo processor which allows full virtualization.
It works quite well with the [Virtue Desktops](http://virtuedesktops.info/) desktop manager. Virtue has some cool animations when changing desktops, like flipping the screen, or rotating a cube. It is cool to flip over to a virtual Linux display.
There are a couple of problems. It doesn’t seem allow changing the VM definition while it is running which is a problem for changing devices, network configuration, or mounted CD images. VMware allows changing devices on the fly. Even the free [VMware Player](http://www.vmware.com/products/player/) allows enabling devices, including USB ones. It also only supports bridged networking. This is a problem at work since the wireless access point only allows a single IP address per login and bridged networking gives the VM a separate IP address. VMware supports NAT networking.