Have a look at these 2 videos: Video: http://www.youtube.com/watch?v=ijBa3XQ_Cco Video: http://www.youtube.com/watch?v=e9D4ftOusLY
Yes I have, the wife and I visited the graveyard of the church below only a few miles from our house. http://www.historicghost.com/HellsChurch.html
If it took you 5 minutes to dig a 6 foot grave(which is insanely fast even with a backhoe) then it would have taken you 9,512 years to dig all those graves(and thats without stopping to sleep eat or pee) So you would've had to start digging way before 1 billion people even existed, not to mention that over those 1000s of years, some of the graves would've probably caved in on themselves from rain/wind/ect.