Recently, I started using IM over a VNC connection on my laptop. And I'm beginning to see a major downside: if I fall asleep in the middle of IMing (yes, I am often that tired), I'll never know about it, and people will still think I'm online. (Apologies, then, if you see me online but I don't respond for many hours; that's the most likely cause.)
All this because my laptop has an auto-suspend function, and because all my VNC-related port forwards are on my laptop. (If your computer gets suspended, all active network connections die.)
In the past, back when I logged in on my desktop, this problem didn't exist; an active network connection meant that any sounds that my IM program emits will continue to play via EsounD (an audio-over-network system), and that's usually very good at waking me up, because I set the volume fairly loud.
So today, I moved my port forwards to my desktop machine. This has the additional benefit that if my DSL connection goes down, my port forwards (and hence my VNC connections) will stay up, since Unix systems seem to have a much more generous connection timeout than Windows does (or maybe I just don't know how to tune the timeout on Windows).
Hopefully, from now on, I'll have fixed the problem and this sort of thing won't be happening again. We'll see. Having said that, I'll be online on much fewer nights now; being kept up till 2 in the morning isn't really my cup of tea, I'm afraid.
On the other hand, if you really want to talk to me, just send me an SMS saying so, and I'll go online. Just for you. :-)