I don't know, that's one of the biggest benefits of Dropbox, I tell someone I'll add a shared drive and 9 times out of ten they already have a Dropbox account (in my tech world bubble at least)
Sure, I have a google account. I almost never use it. For me, the epiphany came when my adsense account was suspended years ago. For what I never found out. I appealed and was reinstated. I then pulled adsense from every site. Lesson learned, and I don't need to learn it again.