Get useful system stats

The name of you Mac is displayed in the login window below the words "Mac OS X". Since Mac OS X 10.6.1, you can click on the name of your Mac to show different statistics about your machine. Each time you click, it will cycle through different bits of information that are particularly useful when troubleshooting problems.

The order of the statistics are as follows:

One click: Your OS X version number (e.g. Version 10.6.1)
Two clicks: Your OS X build number (e.g. Build 94KM1)
Three clicks: Your mac's serial number (e.g. 47HY74G9LNG)
Four clicks: Your mac's IP address (e.g. 196.254.0.1)
Five clicks: The status of any networked account
Six clicks: The date and time (e.g. Saturday, OCTOMBER 24 2009 4:02:31 AM GMT)
Seven clicks: Back to where you started, the name of your computer.

So you click a few times and set the information line to your favourite thing, but next time you log in, it has changed back to the name of your mac. To change the bit of information that appears first, you need to do a bit of tinkering in the Terminal (Applications/Utilities). Open Terminal and type the following command:

sudo defaults write /Library/Preferences/com.apple.loginwindow AdminHostInfo HostName

Depending on which piece of information you want displayed, replace HostName with one of the following:

SystemVersion
SystemBuild
SerialNumber
IPAddress
DSStatus
Time

After doing this, hit return, and the next time you view your login window the information you chose will be displayed. To change it back to normal, simply repeat the command with HostName at the end.