It must really depend on which browser and probably which plugins you use. I use the most current Firefox plus AdBlock Plus and Ghostery (both set to block just about everything) and the screenshot I posted comes up where it's clear that one of the choices is the 5GB free account. What they don't tell you on that page is that you get 6.1GB after signing up (from using a current user's link plus completing a few simple tasks), and if you get others to sign up you gain another 500KB each up to a max of 32GB for a totally free account.
And it works well with the limited Kobo Glo browser, so it should work with any ereader browser. It's a much better option than DropBox even right off the bat since it has 3x the storage space to start.