If you have done autosomal DNA testing with FTDNA (Family Finder testing) you are in for a treat. They have just released Origins Version 3 which uses 90 reference populations from around the world to match with your autosomal DNA. This algorithm basically attempts to estimate your relative ethnic composition (45% Great Britain, 12% Ireland etc) based on your autosomal DNA. In my case this version is a vast improvement over the previous FTDNA versions - which were for me pretty much useless in terms of veracity. The new version provides a much closer estimate to what I can deduce from my genealogy. I think there is still a bias towards Scandinavia thoush. I was also surprised by an estimate of 6% Greece and Balkans.
Another criticism relates to the ethnic categories and maps that are provided and the inferences a casual user might derive. Ireland is broken out as a separate category, but most of Scotland appears within the Great Britain cluster. The Scandinavian category is mapped as just touching northeaster Scotland. The issue here is that generally Highland and Island Scots are most closely related to the Irish or the Norse - rather than the more Saxon, Norman and Flemish dominated Lowland Scots and the English. Now, of course using modern reference populations these more ancient relations become obscured.
In any case, FTDNA Origins Version 3 is a big improvement. This comes right on the heals of the improved version of ethnicity estimating provided by Ancestry.com. If you have not done autosomal DNA analysis I highly recommend you have a go. Also - to maximize finding distant cousins, testing the oldest generation in your family can be an advantage when running an autosomal search such as using Family Finder.