Several of my Skype contacts appear to spend all day logging out and in again. I've asked them and they're not really doing anything, but my Skype app continually notifies me that they've just come online.
I get irritated with notifications about them, and they get irritated with notifications about me.
It appears to happen both with contacts who are using Windows and contacts who are using Ubuntu.
I am behind a corporate proxy, and so are (some?) of my contacts.
UPDATE: I know I can turn off notifications of others logins, but I'm more concerned with people seeing my logins popping up all day.