Hi Terri!
It's a good and valid question you ask and I will try to answer it as good as possible from my point of view.
It all comes down to how good your sources are, what your information is and how much you trust them.
Most of us in Western Europe and Northern America can pretty easy trace our ancestry back to early 1700 or late 1600 by using church records. Before that we have to find other sources.
If you haven't reached noble famlilies, royal families, clergy or people working high in goverments before the 1500, it's more or less impossible to trace your ancestry before this time. Most farmers, peasants and plain workers didn't leave any records for us to find.
Before 1600-1700 you had to do something out of order to leave a mark in history. Either you had to be in a high position familywise or workwise, or you had to have done something illegal and got punished for it.
It gets even worse to get through the Black Death plague that was around 1350. Around 60% of the population in Europe died, and it didn't matter wether you were rich or poor. Most sources before 1350 should not be taken literally, because there is a lot of stories that are not completely true. Only sources written at the time events happened should be trusted. For instance, Snorre Sturlason that wrote the norwegian kings stories between year 850 and 1177 should not be trusted because it is written a long time after the events. The book is in norwegian called Heimskringla and it is written between 1220-1235. Most of it is fiction.
Since I'm talking about books that tell stories about old times: The Bible, The Qur'an (Koran) and other religious texts that are written a long time after the events should not be trusted.
According to Geni God is my 60th great grandfather: Private then he/she should be living around year 80. That is 80 years after Jesus supposedly was born, as long as a mean age with childbirth is around 30 years. In my view it is impossible and something here is wrong.
Harald Haarfagre http://www.geni.com/people/Harald-H%C3%A5rfagre/3950516705030063754... is one man who supposedly got the whole kingdom of Norway under his rule. He lived approx between 850-935. According to Geni he is my 27th great grandfather, that should meen he was living around 1100 if we give a normal lifespan of 30 years between generations.
You are my 22nd cousin 6 times removed. Since you are only 9 years older than me, it is impossible that we can be 6 generations apart. Our common ancestor is http://www.geni.com/people/Harald-Bl%C3%A5tand-Gormsson/54738826920... Harald Blaatann Gormson and he is my 27th great grandfather, I wonder what he is to you?
Since he is my 27th great grandfather (30 generations from me), it gives a mean age of parenthood of 34.2 years for every person between him and me when next generation is born. That is even too much for 2010.
So, how accurate are these trees? Much of the big tree before 1550 need better sources to be proven right. Biblical tree? Well, I do not think the Bible is proof enough of to say that tree is right, but I haven't been much interested in that part of the tree either. I have enough to work with after 1350.
My opinion, as a pretty serious genealogist, is that if a line is not proven with some credibility, then that line is not to be taken seriously. I know I'm going to be peppered by this statement, but if you can't prove som degree of throuth in what you are printing here on Geni, then just leave it out. I do not see any purpose in bragging about that we are descendants of this and that if it's just a lie.
Sources and how much we trust them are the most important thing we do in genealogy, too bad the managers of Geni haven't understood that yet, and given us an uppertunity to add sources to our data. That is without no doubt the most important thing that is missing from this program yet, and until it is implemented all of you are advised to keep your genealogy data on a real genealogy program on your local harddrive. In my opinion, and maybe a come out a bit strong, but until sourcecitations are implemented, Geni is not a real genealogyprogram and should just be used for the fun of it..... :-)
Remi