Michael Boyle sums it up nicely in The Guardian:
That Sadr's return holds out the prospect of a return to violence or increasingly illiberal government in Iraq is clear. But it is also now clear that events in Iraq have slipped out of the hands of the US, turning America into a bystander in the aftermath of a war of its own making. Whether Iraq will continue to consolidate its fragile gains, or slip back into violence or authoritarian government, is a matter that the Obama administration may find very hard to influence.Likewise, Robert Grenier in al-Jazeera:
It is tempting, and perhaps accurate, to ascribe the peaceful return of Iraq's prodigal son to a healthy evolution in Iraq away from violence and toward electoral and factional politics as a means of reconciling the country's deep divisions.
The trepidation which attended al-Sadr's first post-return speech this past Saturday, however, suggested that this transformation remains both tenuous and reversible.
Iraqis do not fear Muqtada's control over 12 percent of the seats in the Council of Representatives. What they fear is the cult-like following which he still commands among the poor, urban Shiite proletariat, perhaps the most potent, least sophisticated, and most manipulable force in Iraqi politics.
Muqtada's standing among this element of the populace would be enough by itself to make him a political force to be reckoned with.
But the real base of Muqtada's power, now as before, is the potential for mob violence posed by his most passionate supporters, as well as the more directed and disciplined threat posed by the Promised Day Brigade, al-Sadr's post-Mahdi Army militia.
Despite its leader's supposed new-found political respectability, an aura of violent illegitimacy still clings to the al-Sadr Trend: Indeed, at least two Iraqi laws bar organisations affiliated with a militia from political participation. The clear lesson for everyone concerned is that accountability under the law still does not apply to Muqtada al-Sadr. . . .
his reiterated opposition to foreign occupation and his insistence on strict adherence to the agreed timetable for US military withdrawal contained, depending upon one's interpretation, either a clear threat, or a familiar and characteristic ambiguousness on the potential for a return to violence.