The new "death-star" styled "subscribe" hover popup (when you mouseover a tag): Does it really need to show us that it's loading? It doesn't bring any benefit, and to me mild irritation. Can it not be shown once the content has arrived rather that blatting the page with a big black stripe of pointlessness until the AJAX request has caught up? Perhaps loading might be demonstrated in a less intrusive manner. It's really rather visually disturbing for such a (to my mind) low priority feature. I think it's the 2-stage delivery that grinds the most.
The benefit that it brings is it shows an indication that something is happening in response to your action of mousing over a tab. While the actual content appears essentially immediately for me, on a slow connection it would be counter-intuitive for there to be no loading indicator. It would be very frustrating to mouse over a tag and have nothing happen only to have it appear in a disjointed manner.