I'm descended from Charles Martel, too. But so much can happen in the way of indiscretions through all the unions going back that far it's just fun to think about. I shouldn't take any of it too seriously and, even so, I'm sure most of my ancestors were peasants or more recently farmers.
If your descent from Charles Martel is through Henry I or Henry II, you are probably related to Obama because he is descended from them.
Here is a great site I find very credible to run your royal ancestry down if you have a gateway American ancestor:
http://www.genealogics.org
Don't let the fact that it is an Australian site put you off. I met the gentleman who owns it and also a 9th cousin who was very knowledgeable on the rootsweb Plantagenet newsgroup.
If you have American Farwell anestry, it is almost certain you have royal ancestors. The gateway ancestress is Olive Welby who was married to Henry Farwell, a simple tailor. I have them 2 or 3 ways but can't find sufficient proof how the lineage goes.
IF you are really interested Gary Boyd Roberts' RD 600 is one of the best sources to check if your tree has American Royal connections.
That is what I recommend to those who choose to attend my genealogy class.
My path goes in by the Douglas family. They say that everyone is related to Charlamange which is not always true but it is close. All presidents are in two families and are related. I am related to several presidents but not closely. I am like a 10th cousin 10 times removed from Clinton. I have about 6 lines back quite a ways and all of them are through the female lines. This is also quite unusual. I have a cousin that was an Admiral. A first cousin 6 times removed was killed August 27, 1776 at Long Island. All of that was without DNA. I have 32 4th cousins though DNA though.