If you click on the "ICQ" button (sorta the start button) and hold down while dragging the mouse, the button while be seem to be stuck in when you release the button.
"Do Not Accept" is spelled wrong for a Phone Call Request.
If you add a "-" in front of your nickname, then restart ICQ 'Nick Name, First Name, and Last Name' will be changed to 'Category, Company, and Department' on your info screen. Also, if you add "&-" instead it will change 'nick name' to 'chatroom' instead of company and not change last name.
When the ICQ server is down, you can sometimes force your way on by rapidly clicking "offline" and "online".
This page will be updated at a later time. More will be added when I find it. None of this is my discovery, most of it is taken from someone else's file of tips and tricks.