Shoutbox

If you're not online, then such a script wouldn't work either...

And if you are online (in whatever status), you can always revert to your event log and sort on contacts comming online.

If the argument is that after a crash or something you still want to know who came online before the crash, then again the events log will fix this since it can be saved to a file....

I don't quite see the purpose of the email notification either... Except for the case that you're far away from your computer (other town) and you need to keep track of who logs in. But in that case, a remote handling script can do this too, or even remote assistance, or any other remote tool or variant...