I have been using the Webmaster tools for years and the average position reported for Search queries is way off for at least one of my sites, which I can easily verify.
The site is not in english and receives great traffic, scoring extremely well seo-wise. However, even for keywords that it constantly appears on the first 1 or 2 places in search results, the average position reported in webmaster tools can be anything from 5 to 30(!).
I am well aware of the fact that search is personalized and results vary (especially if you log-in), but the differences are in many cases vast. Moreover, localized search is not a factor as the keywords are not in english and thus only visitors from my country can use them.
Any thoughts on this? How accurate are these numbers?