You need to add this whole message from this point up the tree onto your site front & centre.

-"Slow, costly internet connection? Save your bandwidth and download quotas by..." (identify problem)

-"Our service saves files from the internet directly to your dropbox without using your connection" (how it works)

-"Spending $x per yGB? At $4.99 per year you can save $z" (value proposition

-features (esp security), how it works (diagram?) pricing/signup

Good luck & congrats on your launch