Joel Wing brings us the latest:
Sadr and his followers have played their hand well so far in Iraq. They have allegedly been promised seven ministries, and an unknown amount of jobs for coming out for Maliki. They are now pushing their agenda further by demanding that Maliki form a national unity government, while letting him know that if his rivals come up with a ruling coalition they will go with them instead. By setting further conditions, the Sadrists hope to not only get concessions, but also be a real power player in Iraqi politics.
Earlier analysis by Wing here.