Apple rejecting applications that use Dropbox
 

Apple is rejecting applications that use Dropbox because if the user of such an application does not have the actual Dropbox application installed, he is presented with a Dropbox login form through Safari, which happens to also show a sign-up link, and after clicking on that sign-up link, users could potentially run into one of the paid Dropbox options. Application developers and users surprised by this may need to read about the frog and the scorpion.

http://osnews.com/story/25898/Apple_...at_use_Dropbox