Sure enough, like a lot of people predicted,

Since the start of the Eyjafjallajökull eruption, which caused cancellations of thousands of flights in Europe because of a giant ash cloud, there has been much speculation about neighboring Katla.

An initial research paper by the University College of London Institute for Risk and Disaster Reduction said: "Analysis of the seismic energy released around Katla over the last decade or so is interpreted as providing evidence of a rising ... intrusive magma body on the western flank of the volcano."

"Earlier seismic energy release at Katla is associated with the inflation of the volcano, which indicates it is close to failure, although this does not appear to be linked to seismicity around Eyjafjallajökull," it added.

"We conclude that given the high frequency of Katla activity, an eruption in the short term is a strong possibility," the report said. "It is likely to be preceded by new earthquake activity. Presently there is no unusual seismicity under Katla."
And since the eruptions at Katla have historically been bigger than those at Eyjafjallajökull, it will get really nasty if it does indeed erupt.
Icelandic President Ólafur Grímsson has warned governments around Europe that a significant eruption at the volcano is close. "We [Iceland] have prepared ... it is high time for European governments and airline authorities all over Europe and the world to start planning for the eventual Katla eruption," he said.
Uh, yeah.