Well certainly the search results are not scientific proof. That's just silly, lol.
I tend to agree with mmasny though. Some sort of survey would be nice. Another way, though would require a bit of coding in the website (not too much) would be to add an extra column to the idioms reference section (
btw good point about this being a 'reference' section). The column would be something like "Have you heard this idiom?" and if clicked (for each idiom respectively) could popup a little window with two more questions:
1. Where did you here it? (Southern USA, Western USA, Eastern USA, UK, Canada, Australia, etc)
2. In which era do you think it most commonly used? (1940s, 50s... 90s, 00s, etc)
Just an example, but good feedback everyone. Thanks! :)