This Geeklet displays a list of your Skype contacts that are currently online. It requires that you save an AppleScript file on your Mac before it will work.
Download this AppleScript and save it in ~/Documents/Scripts. You can save it elsewhere, but you will need to modify the path in the Geeklet script to match it.
Next, download the Geeklet file (linked below) and double-click it to open it up in GeekTool. If you have saved the AppleScript somewhere other than in ~/Documents/Scripts/ you will need to modify the address in the script.
The script fails to run the first time, when Skype asks for permission for AppleScript to access your contact data. Select "Allow this application to use Skype" and click OK. You may need to restart Skype and GeekTool after doing this before the script will run properly.
The script displays the names of your contacts and their "mood messages" if they have any. If you want to disable the mood messages, you can modify the AppleScript. Double-click SkypeOnlineUsers.scpt to open it up in AppleScript Editor. Near the end find the line that says:
set end of onlineusers to aUser & " (" & amoodtext & ")"
change this to
set end of onlineusers to aUser
then save the script.
I originally found this script via this LifeHacker post that links to the original author's blog. Unfortunately that blog no longer exists but you can view an archive of it at the Internet Archive Wayback Machine.