My Dual G5 desktop runs a local copy of Geeklog, so I do all the previewing and editing of stories from its database on the G5. When working on the PB, I enter the G5's IP address to load the submitted stories, preview my edits, and then publish to the G5. (Later on, I dump the SQL data files from the G5 and upload to the web server to publish the hints.)
I was doing this the other evening when the G5 suddenly stopped serving pages. So I put down the PB, walked over to the den, and found that the G5 had decided it was time for its pre-set "sleep if idle for 30 minutes" timeout. But clearly the machine wasn't idle -- it was serving web pages to the PowerBook. I guess, though, from the system's perspective, this didn't show as activity as far as the sleep schedule was concerned (no mouse movement or screen updates).
I didn't really want to disable sleep on the G5, so after a bit of expermentation, I found the solution: to keep a networked machine awake, you simply have to connect to it via file sharing. On the PowerBook, I mounted my home directory from the G5, and went back to work. Hours later, the G5 was still awake. I unmounted the drive when I was done, and the G5 fell asleep again as scheduled.
I assume there are other tricks to keeping a "non active" networked machine awake (setting a cron task to do something every so many minutes?), but this one worked for me.

