In the case of Smentek v. Dart, (pdf) the Seventh Circuit had to answer whether denial of class certification by one judge had any preclusive effect on a subsequent motion for class certification before a different judge in the same court based on similar facts and contentions.
The answer is, apparently, “no.” The case had to do with attempts to have a class of prisoners certified to challenge, as a group, the Cook County Jail’s allegedly inadequate provision of dental services to inmates. Two judges of the Northern District of Illinois had previously denied a request to certify a class. Drawing a third judge, a similar request was granted. The Seventh Circuit stressed that it was not, at this juncture, answering the question of whether the third judge was right or the first two judges were wrong; merely that the decision of the first two judges did not preclude the third judge from deciding differently.
Pretty good opinion. If comity were somehow binding, there’d be a lot less appellate courts.