In the world of product branding and trademarks, companies pay people to make sure they're not stepping on toes and opening themselves up to be sued. To have a product that does the same thing and is called almost the same thing is pretty sketchy. The smartest thing for Dropbox to do is just rename it, especially since it hasn't launched.

If Dropbox is not aware of every competitor and their products in their market space, someone isn't doing their job very well.

How can you properly respond to your competition when you are ignorant of your competition's existence?

A company of Dropbox's size most certainly has a legal department that does, among other things, trademark and patent searches for upcoming products.

How is it fair use to use your competition's trademarks in branding your own projects? If that's the case, I've got a Googl search engine I'd like to sell you.

A search engine spider may not be able to understand this kind of subtlety though, let alone parody.

When people name their company generic words about their product, that's what happens.

Show some creativity if you want to be uniq.