Does Skype work for the Guest login? Skype works fine when I launch it on my Login.  When I switch to the Guest login, though, Skype launches but does not connect after 90 seconds.  Does it eventually connect if I give it more time, or is there some architectural obstacle that prevents using it as Guest?
You say that you 'switch' to the Guest login. Are you using fast user switching and leaving Skype running on your other account? It may not be a problem with the Guest account, but with trying to run multiple instances of Skype on the same machine.