There's a "publisher discussion" subforum here (https://www.writingforums.org/publishing/publisher-discussion/), but it's pretty limited. You can get some opinions at Preditors and Editors (http://pred-ed.com/peba.ht) or a chattier approach at the AW Water Cooler Bewares, Recommendations and Background Checks. (http://www.absolutewrite.com/forums/forumdisplay.php?f=22)
Preditors & Editors is a good way to find out if a particular publisher has a bad track record. Googling the name of the publisher can also be very effective. Duotrope does collect feedback about publishers, but I believe it's limited to things like response time and whether the response received was personal or not.