How about adding a notify system so that when someone who is in your notify list logs in, you get a message that he has logged (if he ever gets visible in your who list). Thoughts, comments?
Be constructive please.
ktnx 
A notify system?
It already is like that for Cabals whether you can see them on who or not. Though a nifty idea, has quite a bit of potential for abuse. If it were meant for like clans specifically, it'd be kind of nice for at least Cabals that are more prone to greet their fellow clan mates. If it were used for just anyone though it'd have to have some kind of fail safe such as being able to accept someone whether they're able to see them log on or not, otherwise someone could just do it to an enemy and when they see it they could log off. If both people accept it though, it should still have some kind of back out deal where you could terminate the process of someone knowing whether or not they logged on or not by a simple command. Not really something necessary so I doubt it'd get put in, and I'm sure a lot of other people would agree with potential abuse as well.
Stop being lazy. Just type whois a lot if you want to see them that bad.
You could even set up a tick timer that fires off ever two minutes like this:
whois ;whois ;whois
You get the idea.
I actually really dislike this because it means that a ninja/thief/ranger/bard who wanted to stay out of sight as much as possible would, no matter what, invariably have his presence explicitly stated to everyone (it's simply not possible to be hidden/camoed 100% of the time, but you can get close). When all you can see is 20 out of 21 people, you don't know who that hidden guy is... he could be level 4 or he could be level 50. This way you'd just put every rogue you see on your notify list and walk around knowing that the instant you'd be able to check who it is you'll be told.
You can easily get around that by making it have to be a mutual agreement by both characters.
Dont like it. Why would you need to?
if they want to be seen you will have seen them on teh who list and if they dont want to be seen you shouldnt get a notice if they pop out even if they do or dont agree... Because then they wouldnt agree to a mutal thing.. So it would just be pointless.. because if they wanted to be seen they just wouldnt pop out.
Round about I know. Shhhh.
You can easily get around that by making it have to be a mutual agreement by both characters.
If someone wants you to know they're on, they can simply send you a tell when they log on. No reason to bother coding it in.
Against it, for same reasons as already stated. Keep the creativity flowing though.