Just discovered this cool trick with Trillian. If you have someone on your contact list, and want someone else to know that they have signed on, you can set Trillian up to do it for you. You may wonder why you would want to do this. Well two reasons. First, you can. Second, if you are using a IM tool like Yahoo, which notifies someone that you have added them to your contact list, by using Trillian this way, you can set up your copy of Trillian to alert another user (not you) that they have signed online.
Given that I like using X's and Y's, it would work like this.
Person X is on your contact list already. Person Y is also on your list. Person X is not on the contact list of Person Y. I set up my trillian to notify person Y that person X has signed online. This way Person X doesn't know Person Y knows they have signed on.
Of course, this defeats the purpose of communication … but it was something I tested out and it worked. How fun!