No one knows how many people seriously use the Internet, right? Pshaw. I can give you bounds on that number in the US, easily.
Snakes on a Plane‘s US gross: $31,561,108
Average US ticket price for 2006 (estimated): $6.60
Number of people seeing Snakes on a Plane: 4,780,000
So roughly 4.4 million people, or about 1.5% of the current US population.
Don’t you love Fermi problems?