The world growth rate has slowed down some since the 60s, largely due to the economic modernizations someone mentioned earlier. The current doubling time is roughly 50 years - http://www.globalchange.umich.edu/globalchange2/current/lect...

As you can see here - http://www.zetterberg.org/Lectures/l96bTab/doubling.htm. More industrialized regions have slower growth rates. Africa will double in just over 20 years while North America will double after over 100 years, for example.

Many countries, like japan and Italy are finding their population is actually shrinking, this tends to be bad for economic reasons. The US gets a lot of population growth from immigrants which keeps the country growing despite having only about 2.0 children per family (2.1 is optimal for maintaining a steady population.)