Things have changed. Gone are the days when I'd instant message my roommate who was sitting at his desk about 3 feet from me to ask about dinner. Gone are the days when you'd spend as much time checking someone's away message as you would talking with them. Gone are the days when you'd keep old friends on your buddy list, though you haven't actually spoken with them in months or even years, but enjoy their away messages. Most representative of my current age...gone are the days when your buddy list had over 80 people (70 of which were online everyday) and there was excitement when new emoticons became available.
These days, when I do sign-on, my buddy list is much smaller and no more than 7 or 8 people are usually online. The reality is for all of the good that AIM does for communication, it also keeps stagnant and false friendships alive. AIM delays the moment when it becomes apparent to both parties that they need to confront the reality that they'd have nothing to say over the phone. Online conversation pauses aren't awkward because they're expected with everyone multitasking (or at least using that excuse), but those pauses are very real on the phone or worse yet, in person. That's not to say the pauses mean you shouldn't stay in touch, but they go along way toward cementing that the friendship has run its course (if you're like me and don't want a friendship based on AIM). If you haven't talked over the phone or in-person during the last year, then something's amiss.
AIM was also used to leave messages for friends if we couldn't reach them, but with the popularity of cell phones (I didn't get one until fall of 2001), leaving a message for someone on their computer is no longer the fastest and most reliable way to stay in touch. Not only do we have little time to talk with someone on the Internet, but we also don't enjoy the not-really real "realtime" communication it offers. If we want to talk with each other, we'll talk on the phone and if that is too awkward, well, then it's just another friendship that has run out of steam now that all of the college parties have ended.
It might take your AIM-only friendship to realize it, but people change, feelings change, and friendships change - just make sure you stay in touch with those friends who are worth more than just another IM and really deserve a phone call. There's a reason why nobody has covered the lyrics of James Taylor's "You've got a friend" to read, "If you instant message my username...you know wherever I am...I'll log-on...to connect with you again."