I go to a fair number of conferences and it really depends on the conference and its represented tech. AWS Re:Invent was about 50% Windows, 30% Mac 20% Linux, Mobcon (mobile dev) was 30% Windows, 65% Mac, 5% Linux, but PhpTek I would say was 10% Windows, 60% Mac, 30% Linux. I was actually taken back by how many Linux laptops I saw.