So, "Watch" is, effectively, a subset of "Subscribe"? - it just shows up on the box that says "Number of new posts in watched topics" (next to the similar box for subscribed topics).
Bummer. I was hoping that it would allow you to "monitor" a topic - have it automatically pop up new responses as they come in (so you get sort of the IRC/Chat room effect).
And some folks need to stop being fanboys and see the forest behind the trees.
(One of the best lines I've seen on this board lately)