Mathmatically, every ten generations should multiply the number of  your ancestors by 1000.
Twenty generations would yield one million ancestors,
thirty generations, one billion, and forty generations 1 trillion,
however, intermarriage reduces this number significantly.

Having now recorded more than 100,000 individual ancestors in
more than 37,000 families, our family tree is one of the largest on the web.
If you have an Ancestry.com account, or are willing to sign up for a free one,
you ar invited to view our complete family tree.
It is one of the largest on the web, with more than 100,000 entries
 in 38,000 families, some going back more than 2000 years,
with over 2000 royal or notable ancestors from
Europe and the Mediterranean Sea area.

I have been amazed at the number of ancestors
having married cousins both distant and not so distant.
I have found more than 100 different lines to Charlemagne,
"The Grandfather of America", depending on the line,
my 42nd great grandfather.
Since almost every American of European
descent can claim ancestry to Charlemagne,
we are all cousins, back only 45 generations or less.

Tom@mayflowerman.com