With a really big one, the ground heaves up over a large area for a few years before the bang, like a zit tens of miles across:

http://www.ees1.lanl.gov/Wohletz/Krakatau.htm

That doesn't seem to have happened in Nevada (yet), so this cluster doesn't seem likely to produce a Yellowstone-sized eruption. Might well be consistent with one big enough to obliterate Nevada, though.

How far is the centre of these quakes from the Yucca Mountain repository? Blowing the US's entire inventory of high-level nuclear waste into the stratosphere *would* be something for the rest of the world to worry about, even if the eruption was only Mt-St-Helens-sized.

The largest eruption ever that we know about was not all that far away, in Colorado:
http://en.wikipedia.org/wiki/La_Garita_Caldera

Even this slightly smaller one nearly made the human race extinct:
http://hvo.wr.usgs.gov/volcanowatch/2005/05_04_28.html

Seems a good bet that both of those had more warning signs than a few minor quakes.