A spokesman for the U.N. Environmental Program (UNEP) has told reporters to expect an announcement next week that would offer a "credible, sensible review of how the IPCC operates." The decision was apparently made during UNEP's meeting this week in Bali, Indonesia, amid growing criticism of IPCC. It would be the most significant review by outsiders, and could therefore have a significant influence in the court of public opinion.(source)
Eli Kintsch points out that there isn't a formal mechanism to review the IPCC. Although it was established by UNEP and the World Meteorological Organization, the founding documents don't provide any mechanism by which UNEP can oversee or influence the IPCC's operations.
Of course that's the formal, legal situation. Clearly, if UNEP and WMO commission an independent review, it seems very likely that the nations that fund the IPCC's work will insist that most or all of the recommendations in that review be adopted. It doesn't seem to me that the lack of a formal mechanism for review poses much of a problem.
Given the recent challenges to the IPCC's credibility,a thorough independent review is an important way that the public's trust in its scientific assessments can be rebuilt.