21 million seems pretty easy to achieve to me worldwide; every one of my social circles and peer groups, both technical and non-technical, in the US and South America, seem to use dropbox. my parents love it. my wife is non-technical to a fault and can't live without it; she just paid for the upgrade to 100gb because it represents safetey to her of her photos. even my under 10 year old son knows that saving in dropbox means he won't lose his homework assignment.

i think they have a huge, huge opportunity.