I love dropbox and we use it personally and for our company (we are paid subscribers). But it seems to me that this space has fewer barriers to entry than say

I love dropbox and we use it personally and for our company (we are paid subscribers). But it seems to me that this space has fewer barriers to entry than say Groupon. People argue that Groupon has little barriers to entry but the fact is that it cost a lot to sell and get merchants on board. Dropbox is a very unique and helpful product but what will stop the competition from creating something similar and possibly better?