I have been working for more than 3 years on a similar thing. I have to admit that you nailed it focusing on a simple interface with just the essential features. I still like mine better of course ;) but I am overloading mine (notepub.com) with features very few people use, just because I am having fun at it. And I do not have the capacity to expand to mobile apps, so I am kind of stuck. Congratulations! I hope you the best for you.