[ubuntu-uk] How do I know when to reboot after upgrading Ubuntu Server?

[Andrew Oakley]

On the Hardy desktop, the update notification icon handily tells me when 
I need to reboot my desktop for the updates to take effect.

I also run another machine, a Hardy Server with no GUI.

After I have performed apt-get update && apt-get dist-upgrade on the 
server, how do I know whether or not I need to reboot please?

-- 
Andrew Oakley