The brewer extension was conceived on the 2.2.x branch and is still undergoing major redesign. For the 2.4.x branch, much of the StyleGenerator class is being rewritten to make better use of classification functions.
If you are a volunteer we could use help improving documentation of this module. Contributing a tutorial would be a great help.
IP review is underway - known issues: http://svn.geotools.org/geotools/trunk/gt/modules/extension/brewer/review.txt
Remember that the module maintainer is a volunteer, and if you can help test this module please jump on the developers list and help out. Patches may be attached to the above issues for review by the module maintainer.
Although not the responsibility of the geotools module maintainer additional or related issues may be found in the the geoserver or udig bug trackers.
- full migration to new ClassificationFunction and Classifier