I have had 3 people in my family take Ancestry.com's DNA test and I have had excellent results.   On my Irish side (O'Sullivan-Green) I had my uncle who is a direct male descendent, take the test. I have received fourteen 4th cousin matches. Out of those 14, I have been able to tie 5 of them back into my family tree.     I was quite surprised by the results. Because any distant relatives must also take the test to get any results, it is very important to use a service with the largest possible pool of people. That is one of the reasons I chose to go with Ancestry.   In all of my family branches, I have found about 20 new cousins. They are mostly here in the States with a couple still overseas.   My biggest hope is that it may allow me break through some roadblocks I have encountered in my research. We shall see.   Good Luck Stephan Wall