The shutdown of air travel in Europe is nearly complete. And it's not clear how long it will continue; the Eyjafjallajökull volcano has been known to continue its eruptions for months.
The unlucky travelers and would-be vacationers will sort their plans out and the immediate difficulties will pass. But the winds in the northern hemisphere are predominantly westerly, and although the path of the ash may waver north and south a bit, travel to Europe could be affected for some time.
I'm wondering if this is the event that brings home the value of electronic conferencing instead of travel. Volcanoes have affected history before.