Family Search.org
I was reading a thread in this group, but I can't find it.
They recommended familysearch.org
So I plugged into on my mom's side, which is Southern/Anglo.....
The bad: I found a record that showed one of my relatives owned slaves. I was expecting it, but it still hits you, just like it does on TV. I'm sure there will be more of them down the road. (grhh)
The good: Someone did a bunch of research on this family. I've got relatives going back to 1540. A fellow by the name of Simon De Villepontoux De Jaure from Bergerac, Dordogne, Aquitaine, France. (I have no idea where that it is, except that it is in France)
= new reply since forum marked as read
There is a lot of good info there, but also some incorrect info. I have documented proof of part of my family back to about 1600 and some at familysearch had it all wrong. Just don't take it at face value. Interesting discovery and I hope it proves true for France and false for slaves.
On FamilySearch.org and Ancestry.com - or any other online genealogy site, for that matter - there are a lot of inaccurate trees. The insidious part is that many people do not check the information so the inaccuracies spread.
I use both of the sites mentioned for research but I do not rely on other people's trees. I use the sites to get access to original documents. Occasionally if I hit a dead end I check to see if other people have found sources I missed. Too often, the other trees have not checked the data thoroughly and have added information that is not correct.
As for your bad news - I have known pretty much all my life that my ancestors owned slaves. My Mom began researching her family tree when I was a kid. I taught myself to type so I could transcribe wills, deeds, and other documents for her. This was at the same time our schools were being desegregated. Nothing like finding that your xxx great grandfather owned dozens of slaves and divided them up among his children - when you have to turn around and go to school with kids whose xxx great grandparents were slaves.
Cool about the family from Aquitaine! All I know about it is that is where Eleanor of Aquitaine came from. I learned that from The Lion in Winter. 
Even the published genealogies can be deceptive especially those published in the late 1800s. Nearly every one seems to trace their lines back to some sort of royalty. While it is possible that every European immigrant was a descendant of a royal family line, I simply don't believe that every single one can be traced back to them.
As for messed up trees, I have a line that traces back to the Harlan family that bought land in Pennsylvania from William Penn. The original immigrant, George Harlan (or Harland), had a son named Aaron who sired a series of Aaron Harlans. One of the trees I found on Ancestry had one of the later Aarons married to his mother and as his own father. 
Obviously the person who created that tree never actually read the material they were linking!
But FamilySearch.org, Ancestry.com, and other online sources can lead you to some wonderful discoveries. A wife of the first Aaron Harlan came from Mobberly, Cheshire, England. Her family traces back to some of the earliest Quakers - who kept excellent record. On Ancestry I have found scans of the original Quaker records that take the families back to the 1500s. Solid, definitive records, no speculation or creative writing!
One of my husband's lines, the de Prefontaine family, was a dead end with Peter who lived in Maryland and was supposedly from France. I accidentally searched English records on Ancestry and found the will of his half sister in England. She left property to her siblings who had moved to America. Through that will, I traced the de Prefontaines (who were actually named Papin or Pepin but were from Prefontaine) back to their immigration to England as part of the Huegenot expulsion from France. I have not yet delved into the French records but may be able to take that line back farther - if I can translate from the archaic French!
