When you have a moment, please go over to the blog The Legal Genealogist and read Judy G Russell's article "Blown away with DNA." This is a moving passage about a person who was adopted and is now using genetic analysis to find relatives.
Several of my genetic matches in the database at 23andMe were adopted. The only genealogical information they can offer is their own date of birth and location, which does not help when you are looking at connections from the 1700s. By triangulating and clustering my matches, I can usually provide a possible branch in my documented family tree where the common ancestor could be. Seeing the names, locations, and dates of possible ancestors means so much to someone who had no family history before taking the DNA test.
I manage two DNA accounts for people with no family history. One was formally adopted and the other was not. I do not have results yet for the person who was formally adopted; they are pending through Ancestry.com's new autosomal DNA service. The results of the person with no official adoption was through 23andMe's Roots into the Future program. No very close matches were discovered yet, but seeing and exchanging information with distant genetic cousins provides a glimpse into her family's history.