This is one of the Finnish F-18's which went to play with the cloud - note the date:
PICTURES: Finnish F-18 engine check reveals effects of volcanic dust ...
Link is here:
PICTURES: Finnish F-18 engine check reveals effects of volcanic dust-16/04/2010-London-Flightglobal.com
As for rules... sure if there is doubt then no doubt.
but
if there is no doubt then don't doubt too much.
Only IFR are banned ... VFR are not banned ... how does the ash know what the flight rules of the pilot are? Good rules are good ...
........ and sure it's a difficult decision - can this stuff be seen and can safe passage routes be established? How much would it cost ? Is it worth it? Do we care? Could we do better?