700 million people use them, and 17 million are on a paid plan. I still use Dropbox, because I don't trust that I'd be able to reach a helpful human at Google should anything happen to my Google account.
we may have different account types but they started wiping inactive accounts a while back. I never installed the client on my computer though, so that probably didn't help.
I had pictures of an abroad internship from winter 2014-15 that I was able to find last year as I was aggregating all my pictures.
But I just checked their filings, the 700M figure is indeed "registered" users, not "active" ones. Which makes a lot more sense. There are not a lot of services with 700M monthly active users out there.