I'm very curious how quickly Windows 10 is being adopted. One quick way to get a look at this normally is via web analytics and traffic dashboards for large Internet services like content distribution networks. They're ususally slow to make official statements about global traffic patterns, but you can check your own reports and see what's going through.
I checked if the web analytics and traffic dashboards I have access to are up to speed on Window 10 and Edge, and it appears they are not. Akamai's traffic dashboard doesn't list either, perhaps they're under Unknown, and neither does Google Analytics which appears to lump the OS into Windows NT (based on this site's stats). This makes it difficult to see just how many people are actually using the Edge browser and/or Windows 10.
Hopefully this can be rectified quickly. I anticipate that Windows 10 adoption will be much quicker than previous Microsoft upgrades, more on the order of recent Mac OS X upgrades, especially since it's free. But I'd like to know for sure. :)