From your source, "According to OPSWAT’s data (which admittedly could be wildly skewed depending on who actually downloads their software, take it with multiple grains of salt)."

Admittedly I'm referencing data I read somewhere which I can't find right now, so I'll retract the statement about SkyDrive being the biggest. It is certainly up there though and growing according to this financial report.

Almost every windows tablet sold is another user for SkyDrive. I am not sure about Windows 8 and 8.1, but significant portion of those sales will add users to SkyDrive as well. Let's not even talk about Office 365 which forces you to use SkyDrive. So while SkyDrive might not be #1 in terms of number of users, given aggressive bundling strategy, I would expect it to be close to the top in terms of growth.

But as a metric for actual popularity, that is a completely useless stat. Microsoft also used to crow about how many tens of millions of people had Windows Media Center, but most of them were just people who bought a "premium" version of windows with their pc and didn't even know what Windows Media Center was. If gazillions of people are technically users of skydrive simply by virtue of having windows, that really says nothing about skydrive's actual popularity. It's like claiming solitaire is the world's top-selling game.

> If gazillions of people are technically users of skydrive simply by virtue of having windows

Or Hotmail. I don't use Windows, but I use Hotmail and I have some files stashed away on Skydrive. This is stuff I don't access frequently where it's fine to go through the browser to get them.

I even tried it on a Mac, but it needs a case-insensitive filesystem. Amateurs...