My Power Mac G5 2.3 GHz is running slow. How do I speed it up?

Adding memory usually helps.

http://eshop.macsales.com/shop/memory/PowerMac-G5-Memory

Verify that you have several gig of hd space free -- two to three minimum.

Run activity monitor to see what is causing the slowdown.

Some semi-randomn thoughts on addressing performance problems.

Activity Monitor
Look at what is happening with your Mac when you run Activity Monitor.
Macintosh-HD -> Applications -> Utilities -> Activity Monitor
Click on the CPU tab on the lower half of the window to see how much time you are using and if any applications are hogging the CPU.

You can gain some understanding of Activity Monitor by looking at it every once in a while. Look at the small graph.

Here is how I have my cpu display set up:

AppleJack
"AppleJack is a user friendly troubleshooting assistant for Mac OS X. With AppleJack you can troubleshoot a computer even if you can't load the GUI, or don't have a startup CD handy. AppleJack runs in Single User Mode and is menu-based for ease of use."
http://applejack.sourceforge.net/

Console
You can use the console application to examine Mac OS log files. The logs will contain information on various system processes.

Macintosh-HD -> Applications -> Utilities -> Console

File > open console log
this will display the startup messages

and
file > open system log
once the system is started, messages will go into the system log

Other folks
bdaqua advises running disk utility from install disk and performing a safe boot:
http://discussions.apple.com/thread.jspa?threadID=2256611&tstart=0

Allan Jones advises running automatic maintenance scripts and checking for free disk space:
http://discussions.apple.com/message.jspa?messageID=10845311#10845311

K Shaffer advises checking for available RAM and checking for free disk space:
http://discussions.apple.com/message.jspa?messageID=10879449#10879449