Mac Uptime PPC 1.210 has been exactly the solution I was looking for. It's nice to be able to turn on the monitor or connect via VNC to see how long it's been up.

Today I put together an AppleScript ACGI (since Mac Uptime PPC is scriptable) and some Ajax to insert the uptime (and update every 60 seconds) in http://buuto.makkintosshu.com/. Check it out, if you're interested.