I'd rather not tell you the exact text of the tooltip, but it basically shows like this;
Current nickname - (eMail address): Status
Current nickname will only show in the tooltip up to a certain amount of characters - I normally have my display name there (e.g: Paul) follow by a space, followed by a hypen followed by some text if I want to put any text there (e.g: "aMSN rocks! :)"), so putting "testing testing testing" in 10 times after the hypen and space results in the tooltip just showing the nickname only, and the rest just drops off it (although this is probably an Operating System [Windows XP] issue).
eMail address, perhaps obviously, never changes, and is located in brackets.
Status, well, shows the status.
I can confirm that changing ones nickname does cause the text of the tooltip to change and then causes what is effectively a new entry in the Customize Notifications