Dan,
Glazing helps performance. Some of the companies that are glazing the trapway are Toto, Western, Briggs Vacuity and Kohler. Toilets that are using the Sloan Flushmate, work well whether they are glazed or not.
Terry Love's Consumer Report on toilets
http://www.terrylove.com/crtoilet.htm

Terry

• Terry Love's Consumer report on toilets (click here)