Reinhold, a photographer from Heidelberg, Germany, has started an excellent english blog about Caffenol - and his results are just amazing. Some people confirm his findings, including a range of 13 - 14 f-stops with Fuji Acros. He even shows photos with Acros@1600 ASA.
http://caffenol.blogspot.com/
http://caffenol.blogspot.com/