I was wondering the same thing.
Below is a link to an article by Dr. Arpad Vass. He is currently a Senior Staff
Scientist at Oak Ridge National Laboratory and
Adjunct Associate Professor at the University of
Tennessee in Forensic Anthropology. The article appeared in the Nov 1, 2008issue of Microbiology Today.
In the right margin of the 2nd page of the pdf (page 191 of the magazaine), he states "In temperate regions of the United States individuals can be completely skeletonized in 3040 days in the summer."
***Warning, some graphic images of human decomp.
http://www.sgm.ac.uk/pubs/micro_today/pdf/110108.pdf