I've been following a thread in the forums that refers to a very simple change in Ubuntu that actually is improving the responsiveness of many Edgy and Feisty users (including me).
I have no idea why this is, or if it has any side effects, to be careful.
Edit your "/etc/hosts" file: $ sudo gedit /etc/hosts
You should see something like this:
(and if your in Feisty, some lines about IPV6
Now, add the following:
127.0.0.1 localhost martin-laptop
(Replace "martin-laptop" with your hostname)
Save. Should work instantly, or sometimes on reboot.