When you launch Dropbox, you see the first and second layers of information.
A person will be able to open Dropbox with one tap and open any content in Dropbox with the second tap. So a person who uses Dropbox on the iPhone derives significant value within two steps. Once the content is open, a person will be able to derive additional value, say store the document into iBooks for example, with two more taps.
|Launching the content with one tap|
|Acting on the content with two taps|