This isn’t just for virt-manager, but any X-Windows app you’d want to tightly integrate into your daily routine. Instead of firing up X11, then SSH’ing to your VM box and typing out virt-manager (insane!) you can script X11 to do everything with 1 mouse click. I have it in my Dock, and Launchbar also recognizes it as an app.

tell application "Finder"
    launch application "X11"
end tell

set results to do shell script “ssh -X haddad-vmserver ‘virt-manager’”

Sweetness.

Also see my post about setting up a headless VM server using KVM.