Open up the file /etc/hosts with root privileges, e.g. by typing

sudo gedit /etc/hosts

The file will look like this (instead of hostname it will include your host name):
127.0.0.1 localhost
127.0.1.1 hostname

Now add you host name to the first line after ‘localhost’.

So if your host name is ubuntu, the file should look like this:

127.0.0.1 localhost ubuntu
127.0.1.1 ubuntu

You should now notice faster startup times of your applications.

Thanks for this tip goes to psyke83 who posted it in this thread on the Ubuntu Forums.