Coupled with the Growl relay and Avahi (to announce your Linux box as a Growl-enabled box), it's a pretty nice way to have all sorts of notifications visible to all the computers on your LAN, regardless of whether they run Mac OS X or Linux (a Windows version that uses the standard notification bubbles has been on my mind for ages, but realistically I will not be getting around to it anytime soon).
For instance, I have my web server send me occasional reports on load, Referrers, etc.:
[Apache+PHP] -> [home router] -> [Mac mini] -(relay to all machines)-> [Me]
...and a few other local scripts (like an ADSL connection status monitor). It's all pretty trivial to set up, and I'm sure a lot of people will find this useful.
Talking about useful, and although I use the AdBlocker XUL extension on Firefox, I've just come across a really good custom CSS to block most advertisements in Safari. Finally, junk-free browsing without weird plugins.