This is a great story by Amy Harmon in the NY Times:
Stalking Strangers' DNA to Fill in the Family Tree
They swab the cheeks of strangers and pluck hairs from corpses. They travel hundreds of miles to entice their suspects with an old photograph, or sometimes a free drink. Cooperation is preferred, but not necessarily required to achieve their ends.
If the amateur genealogists of the DNA era bear a certain resemblance to members of a "CSI" team, they make no apologies. Prompted by the advent of inexpensive genetic testing, they are tracing their family trees with a vengeance heretofore unknown.
You have to read these stories to believe them -- people stalking possible distant relatives to collect their DNA from discarded cups, scheduling DNA collection visits to older relatives with dementia, and plucking hairs from corpses at funerals.
My mom's here visiting, and she does a lot of amateur genealogy. She says, "There are a lot of nuts out there!"