Ancestry Finder is a program accessible to those that have had their DNA tested at 23andMe. This program takes the information provided by customers of known heritage and lets you adjust the minimum segment length, number of grandparents from a given country and whether to include those from the Brittish expansion (Canada, USA, Australia etc.) and whether to only look at those with Ashkenazi Jewish ancestry. These are my Ancestry Finder Results from 23andMe at the default setting of 7 cM and 4 grandparents as of February 27, 2012:
According to this poster from 23andMe, only highly concordant countries, when found in your AF, are good indicators of ancestry for people with unknown heritage.This research was done by J.M. Macpherson1, B.T. Naughton1, J.L. Mountain1 in co-operation with 23andMe. The authors specificly mention Portugal, Finland and Switzerland but one assumes that Ireland and Greece fairly reliably indicate ancestry while Russia, France and Germany on your AF results are highly unreliable and may indicate only mixed European heritage.
Sources 23andMe Spittoon and Ancestry Finder, Paper by J.M. Macpherson1, B.T. Naughton1, and J.L. Mountain1.