So the latest versiion of AIM for Mac lets you create friendly names for mobile and ICQ numbers you add to your buddy list. Alas, you can't do this for AIM/AOL buddies ... or can you?
Most other AIM clients such as Adium and GAIM now have a feature to let you store aliases for your buddies, and most times these are stored on the server. As it turns out, GAIM and GAIM-based clients store them in the exact same location as the Mac AIM client stores those friendly names for mobile and ICQ numbers. So by going into any GAIM-based client and setting aliases for your buddies, those aliases will show up in the Mac version of AIM.
The catch: Only one buddy can have a given alias... hence if one person is aliased "alex", then you can't have another "alex;" it will simply show up as their screen name unless you set it to something else.
[robg adds: I haven't tested this one...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040620103625138