Thanks, Jedburgh--a useful piece. It is a shame it doesn't devote more explicit attention to this issue:

Although Sistani is still a powerful figure within Iraq, his influence has diminished since the bombing of the Shi‘i shrine in Samarra in February 2006 and the ensuing increase in Sunni–Shi‘i violence.
...which the author raises in the executive summary but doesn't really explore in the report. How much has Sistani's influence diminished? I've read a few items which suggest that he's been sulking because of his declining political weight, but it would be interesting to hear from someone who has looked at the issue from a closer perspective.