I have exactly the same problem with the N9 and the N900. I am thinking it occurred after a skype update for PC last month.
It is odd that it is affecting both devices, but not everyone. I cannot see anyone online. My contacts have disappeared. I removed account and re-added but contacts didn't reappear. I can manually add contacts and they can see me online but not the other way around. Status is "checking". I am hoping someone can shed some light on this.

I have started a thread for the N9
http://talk.maemo.org/showthread.php?t=86045