The Interacademy Council has published its Review of the processes and procedures of the IPCC (press release)
My first impression is rather positive; while recognizing the quality of the reports, significant improvements in procedure, management and communication are suggested. Issues, I value in particular are the transparency in choosing lead authors, the recognition of deviating views (not crack views), rules in assessing grey material, limited terms for the chairs; the suggestion to have a time lag between the physics and the impacts reports makes very much sense. Also the obligation of IPCC to respond constructively and openly to inquiries from the public, including those concerning possible conflicts of interest, is very welcome.
A remarkable quote is: „IPCC’s mandate is to be policy relevant, not policy prescriptive. However IPCC spokespersons have not always adhered to this mandate. Straying into advocacy can only hurt IPCC’s credibility. Likewise, while IPCC leaders are expected to speak publicly about the assessment reports, they should be careful in this context to avoid personal opinions.”
For a more detailed account, refer to the executive summary in the full report; also Roger Pielke jr.'s overview on his weblog is instructive.