The Virtual Machine Manager application (virt-manager) is a desktop user interface for managing virtual machines.
The MacVTap Wiki over at kernelnewbies website has some very useful information on the benefits of the KVM MacVTap device driver.
The kernelnewbies website has a considerable amount of information on Linux virtualization.
Another good option for a virtualization server is CentOS. Nixcraft has a very good article about setting up a CentOS KVM virtualization server. They are using CentOS v5.3.
There is a great Startup guide for KVM with CentOS on ITSC blog. But this time it is the later CentOS 6.0 version and they are setting up a headless server. They add virt-manager to the headless server and run it remotely from a seperate management host–very useful.