Just recently I decided to do a bit of sleuthing, just for fun, on my step-father's family. Being from Kent county I knew I could find plenty of Michigan records to do my initial tracking. What I didn't count on was in a matter of hours to trace one line of the family back to Revolutionary War time using online records (Seeking Michigan and Family Search). A Google book search pushed it back three more generations with a published genealogy.
I ended up following the Farrington line from Michigan back to a man named John Farrington who was reportedly in the Americas at least by 1639.  That's not bad for several hours work. It was certainly exciting for me to follow such a clear lineage and get so far with it (and no, I never looked at anyone else's tree, there really was no need to). Naturally, this is merely the scaffold upon which to build something more interesting than a list of names and dates, but it's a place to start. I only wish my family were so readily traceable. I'm not greedy; I'd be happy with just one line like the Farringtons.
Why is it that none of my family lines were this easy to trace? The luck of the draw, I suppose. In a little over ten years doing genealogy on my own family I have never been able to trace any one line this easily with census and vital records. I ascribe it mostly to luck. Michigan has reasonably good records, prior to requiring birth/death certificates. Massachusetts, because it has more history, has good records even further back (and they are online also). I actually found vital records (birth, marriage and death) for virtually all of the direct ancestors in this line. On top of this I was very fortunate to find parents' names (usually both) on the vital records I did find.
Now that I've done the hard/fun part, I anticipate I'll have a good Who Do You Think You Are moment for the family. Even if they know a little, I'm sure they have no idea they can trace their heritage to within twenty years of the Mayflower. While I didn't find any ancestors who served in the Revolutionary War, I didn't really look very hard. Besides, if I found out everything for them they couldn't have the satisfaction of finding a few of these treasures for themselves.
1. William Richard Cutter, editor, New England Families, Genealogical and Memorial: A Record Of The Achievements Of Her People In The Making Of Commonwealths And The Founding Of A Nation, (New York: Lewis Historical Publishing Company, 1914) 3: 1552-1553.