I think this has been discussed, with lots in the archives, but GMA is more 
difficult to get good IHC staining, since it cannot be removed once polymerized.  Check out
Neil Hands article in J of HIstotechnology, 21(3)1998, he did methyl
methacrylate, totally removable, and stringent antigen retrieval.  

He has a panel of 200 or so antibodies done this way, elegant and very useful
for plastic aficiandos.  MMA is no more difficult to work with than GMA,
depending on the tissue, bone cuts better with tungsten carbibe knives.  Have
seen his slides, really wonderful staining! and was impressed it could be done
by removing MMA with warm xylene.  

Hoods are a must!

Gayle Callis