A totally unscientific technique, and not even my idea (being, as it is, stolen from a colleague who never published 😉 )
However, this is the Google page count, using the site:.tld query syntax:
| site:.com | 7,490,000,000 |
| site:.org | 2,250,000,000 |
| site:.net | 580,000,000 |
| site:.info | 81,500,000 |
| site:.biz | 26,200,000 |
| site:.tv | 21,600,000 |
| site:.mobi | 236,000 |
Interesting though. I guess I should do this every now and then to track change.
(And perhaps also work in length of TLD availability to get an idea of uptake as a function of time).