Based on the small sample size of the current members of the brand new Donor Conceived Project at FTDNA [as of 10pm on 6/14/2011: 15 offspring, 1 donor, 12 Americans], it seems the stereotype of all those jewish medical students/residents/doctors being donors could be true. Almost half (5) of the 12 American offspring have evidence/proof that their biological was, at least ethnically-speaking, Jewish.
The thing that I wanted to bring to light is how this discovery can be both a wealth of information and a black hole of nothing. And it all boils down to luck.
And here are some reasons why, and some things to consider if you a) believe your biological father was/is Jewish, or b) if you receive results that signify Jewish lineage.
[EDIT 7/2/2011 - see comments for source]
The population bottleneck in Ashkenazi Jewry results from the fact that all of the Ashkenazi Jewish population is descended from a small number of founders who moved to northern France and the Rhineland about 1200 years ago.
A more accurate description of the effect of this bottleneck is not that all AJs are fifth cousins several times over, but rather that all AJs are 10th-30th cousins many, many, many, many, many times over.
In other words, this bottleneck existed long before Hitler. We are all (as eastern European Jews) very closely related. A better name of this bottleneck effect is "founder effect" or founder population.
And since the algorithms used by testing companies like FTDNA look at the amount of shared DNA to establish how closely related two individuals are, with an endogamous population like the Ashkenazi Jews of Eastern Europe, they will falsely predict two individuals of being closer related than they actually are because there is so much shared DNA.
Now FTDNA is trying to correct this by tweaking (or possibly creating a new algorithm??) for individuals who appear to have Ashkenazi ancestry, so anyone who currently has Eastern European Jews as matches may find that some of those matches may disappear and other close matches may be moved to the speculative or more distant categories.
The concern with bottlenecking (and actually dealing with any endogamous population...such as rural America and certain religious groups like the Amish that tend to stay in the same place for generations), is that many of your matches might be much more distantly related than FF suggests, as well as related through multiple avenues.
The Holocaust = No paper trails
Obviously the Holocaust destroyed most, if not all, of the records of European Jews. With no records and a bunch of recent immigrants that fled death, the likelihood that your matches are going to have extensive family histories and know all their 2nd, 3rd, 4th cousins is rare. Often they are doing this test to try and find their lost family members who were separated during WWII. They may or may not be concerned with your plight as a donor offspring, but unless the match is close enough to your biological father that they would be in contact today, they probably are just as clueless as you are!
Surnames. Many Jews, upon coming to America were either so overwhelmed that, as the Yiddish story goes, the old man, upon arriving at Ellis Island was asked his name, and he responded "sheyn fergessen" (I forgot). The official at Ellis Island supposedly took that as his name and recorded his name as Sean Fergusson. Now, whether or not this is a true story is neither here nor there. The point is that names change. Especially surnames. Jews (along with many other Eastern Europeans and Middle Easterners during that time period) often felt the need to change the spelling of their surname, or often change it all-together so that they would be seen more as Americans and not discriminated against. It's no wonder that some of the most common Jewish names today are Miller and Brown. This name change, especially a change so recent, could make it nearly impossible to identify your biological father based on the ancestral surnames of your matches, or even on the results of a Y-DNA test!!
But even for the Ashkenazi jews that did not change their names specifically upon coming to America, for most Eastern European jews, surnames as they are seen in Western Europe and America, were a foreign concept to most ethnic groups originating in the Middle East (including my Armenian family). Patrilineal inheritance of surnames was only something thrust upon them by the governing bodies of the lands where they lived in Europe (Germany, Austria, Russia, etc). Traditionally most Jews (besides names associated with the ancient priestly castes: Cohen and Levy) were called by their given name, and to differentiate the word "Ben" (son of) and their father's name was added. When surnames were introduced or mandated, many of the same genetic clan picked up different surnames, often based on the occupation of the head of the household.
So not only might your matches be more distant than FF suggests them to be because they could be your 5th cousin 3 times instead of your 2nd cousin, but that match might not even have any information or surnames that could help you identify your biological father.
However...it's not all bad. The big plus side to discovering or knowing your biological father is/was Jewish (by heritage, not necessarily by religion) is that while most people who sign up for the Family Finder test get dozens of matches, you're likely going to get HUNDREDS of matches!! Due to a multitude of reasons (reconnecting lost loved ones, missing paper trails, and a a great interest not only in personal genealogy but the genealogy and history of their people), there are more Ashkenazi jews that go through genealogical DNA tests than any other specific ethnic group.
That means you'll have a significantly higher probability of matching with a close or immediate relative of your biological father.
So it's obvious that learning that your biological father was Jewish provides you with a lot of potential in DNA testing, but also a lot of frustration. The one thing that I know is that for all my donor-conceived friends who just in the past few months learned their father was Jewish, it gives a sense of identity that was not felt before.
And as I remind myself as go through this testing process, each one of your matches is family. So the idea of finding your family and learning more at least about your deeper ancestral roots, is something to speak for.