I've used Ancestry.com and also the forums at Genealogy.com and found some valid tidbits of data. One day, I went to Genealogy.com and decided to try a new surname, so I searched on my mom's grandmother's maiden name. There on the main page, about 4 or 5 posts down from the top, was a post from someone else searching for the exact same descendant! We connected, and one day while visiting my parents my mom opened a drawer in a small table next to the sofa where she sat, and pulled out an old family photo from that family. I scanned it and sent it to my new family "friend" -- turned out she found the exact same photo in a box in their shed. I also found a 2nd cousin of my dad's in another forum there.

I'm a descendant of William Nickerson, an original settler of Chatham, MA (my great-great-grandmother was a Nickerson). There is a genealogical association devoted to the Nickerson family name which helped me close some gaps and verify the research my ancestors had already done.