I have found that my stouts produce much more foam during fermentation than other beers do. On the Mr. Beer website it says: Plenty of foam, although messy, is not a bad thing as it indicates healthy yeast and a strong fermentation. Excess foaming is more likely to occur when using ale yeast with darker brews and higher fermentation temperatures." (Emphasis mine.)
This confirms my own experience. Question: why is it that ale yeasts fermenting dark styles are so prone to producing more foam in the fermenter?