If this is true, it would mean two things:
1) That the surge and resulting crackdown in Baghdad is having an effect - it's difficult to understand why Moqtada would leave his power base unless events have convinced him that he is no longer secure.
2) Iranian support of Shiite radicals in Iraq would be, well, undeniable.
The aggressively vapid NY Times, of course, has this to say:
If Mr. Sadr had indeed fled, his absence would create a vacuum that could allow even more radical elements of the Shiite group to take power.
Reminds one a bit of we've got to deal with Yasser Arafat because he's really the best of the lot. Moqtada for the Nobel Peace Prize 2010?