Just been called across to help a colleague, and one of the many issues he was having was that the vertical scroll bar had disappeared. Any ideas?

Aha! F1 is your friend :-} but how did he manage to trigger an option as well-hidden as File > Options > Advanced > Display > Vertical scrollbar without noticing? that's the remaining mystery. Alt+F,t,a,Alt+v,Alt+v, spacebar doesn't look like a likely slip of the fingers.