Yellowstone is a "hot spot" that is not connected to a plate boundary hasn't really had the level of activity that would say an eruption is going to happen right now. However is is active and the art of prediction isn't that settled. Katla has the double whammy of being a hot spot and on the Atlantic ridge plate boundary where the ocean floor is spreading. Frequent volcanic activity is a given there but not as destructive usually as a super volcano like Yellowstone.
What I am waiting for is a totally new volcano somewhere like Parícutin in Mexico where, in the 1940's, one day a guy was plowing his corn field and literally the next day a crack in the earth opened up and a volcano was born. That sort of a thing could put you off your feed for a while.
Around the end of '08 beginning of'09 there was tremendous seismic activity at Yellowstone. Back a few months ago there was another set of quake swarms, that the USGS says was larger than last years.
The floor of Yellowstone Lake had been lifting in the past. What is happening now, I'm not sure.
Though not in a subduction zone, should something start this thing up, it could make an eruption in Iceland seem like nothing more than a burp.