And then the iPhone App Store launched, which turned out to the be the perfect distribution and application platform for the software. By November 2008 they had 500,000 users. And recently the Times reported Evernote had surpassed 2 million users - fully half of which are iPhone users.
As usual, there may be other confounding factors that explain the growth, so this is not conclusive. But it does reinforce the importance of persistence in entrepreneurship and the introduction of new products.