The derivation of the dataset is described in this publication <http://www.the-cryosphere.net/6/221/>. In it, issues of uncertainty and heterogeneity are discussed in detail. These are especially important when using such data for validating other models. Updated statistics for global/national permafrost areas as well as plots detailing the nature of permafrost areas in terms of latitude, elevation, heterogeneity and terrain ruggedness are available and include an estimation of uncertainty.
PS: I have no idea how the GIS server performs when subject to many parallel requests. If Google Earth of the Web Mapping Service become slow, please retry after a few days.
Stephan Gruber ([hidden email])
Department of Geography, University of Zurich
Winterthurerstr. 190, CH-8057 Zurich, Switzerland
phone: +41-44-635 51 46