An editorial by Mike Rossner, Heather Van Epps, and Emma 
Hill published in the Journal of Cell Biology 
(http://www.jcb.org/cgi/content/full/179/6/1091)
is a very disturbing report about their inability to verify 
published impact factors  using data provided provided by 
ISI itself. Their fruitless efforts to  replicate published 
impact factors for their own and other journals revealed 
numerous and serious errors in several data sets provided 
by ISI and call into question the validity of both ISI's 
dataset and their published impact factors. Published 
impact factors affect authors' decisions about manuscript 
submission, funding awards, and promotion and tenure. 
Though there has been some criticism about impact factors 
in the past, this is the first time a serious question has 
been raised about the underlying validity of the data used 
to calculate impact factors and the accuracy of the metrics 
that are published.