The PowerMac G5 was the first system developed by Apple that came with a liquid cooling mechanism for the models with higher-clocked dual PowerPC chips. In most systems, this cooling system worked well. To this day, my system has not shown any problems; however, some systems had an issue where coolant leaked, causing corrosion and shorting out mainboard components.
For a while Apple had a replacement program for the G5 in the event of coolant leaks, but if your computer develops problems with the cooling system now, you will probably not be able to get the computer serviced. Apple has the G5 on its vintage list, which means you can still get parts for the machine but Apple has discontinued providing hardware support and service for the computer unless you are in California, where you may still get parts and service until the computer is declared obsolete--seven years after discontinuation of production.
To help people fix problems with their cooling systems, numerous take-apart guides have been created showing how to disassemble, clean, fix, and reassemble leaking cooling systems. Recently, an exceptionally detailed six-page guide was posted on xlr8yourmac that shows what to look for and how to clean up and fix coolant leaks on these systems. The guide specifically uses the 2.7GHz model, but it should apply to all systems using the liquid cooling system.
In other news Apple has recently released updated installers for the 10.6.4 update to OS X Server. These updates include fixes to problems with the Wiki services that appeared in the original 10.6.4 update for OS X Server.
If you have already applied the 10.6.4 update for your server, you can either reapply the Combo updater to include these fixes, or you can install the Wiki Server Update 1.0 patch that should address the problems with the Wiki services.
Keep in mind if you highly customize your server setups, you may want to be cautious when applying updates since they can more easily break those customizations or any work-arounds you have implemented for overcoming limitations in various built-in services.