In the US*. The Bitcoin paper has surely been distributed far wider than any US-specific tax forms.
Edit: Now that I think about it, the W-2 probably is even larger than 1040, because you get one from each employer, plus families can file jointly, and not everyone has to file taxes if they make below a certain amount. So a household with 4 people working 2 jobs each generates one 1040 but 8 W-2s per year.
For Google search numbers, that would be different considering PDF searches in China wouldn't be done using Google. But perhaps taxes aren't done using PDFs either, that important detail I don't know.
Basically anyone who ever opened investment account know about it.