I've spent a significant portion of the last two months working on an app called Noted. Noted is an outline editor built for speed. It was inspired by my frustrating experiences with apps like Evernote and Notational Velocity, which, while powerful, were often cumbersome and difficult to manipulate - not attributes you want while trying to take notes in a lecture where the professor is talking much faster than you can keep up with!
To be sure, there are quite a few hacky bits littered throughout the source code: dealing with the strange complexities of models that might or might not be loaded, routing that sometimes doesn't reset state to the degree you'd expect, and having templates relying on complex state in a templating language that doesn't offer more than a boolean "if" statement. But these "hacks" are no worse than the "hacks" you'll see in Angular JS or even some Backbone applications - sometimes it's just not worth finding the more elegant solution, as long as you leave the ugly one well-commented!
I built Noted at Hacker School, which has been an absolute blast. It was wonderful to get constant, positive feedback, to have an immediate group to help test and give suggestions on usage of the app, and to be able to focus on just coding for the first time in my life, rather than trying to fit around traditional academia like I had been doing for the last two years. In fact, I'd tried to build this application before last year, but failed miserably because I couldn't find the time I needed to really learn how Ember worked (leading to an ill-advised custom build system and a horrible, over-complex architecture).
This time, while I kept the base styling from a year ago (that is, gradients I eyedropped from Mac OSX window panes and a kind of ugly yellow), I went into this with the knowledge that I could spend time really learning Ember. I also found many aspects of the framework to be much more built-out than last time I had used it, with Ember Data's associations being much more elegant and Ember's routing not being a complex trainwreck. I also built it on Rails, which I'm primarily using as a powerful build system, thanks to the asset pipeline. While there are some Grunt plugins that can handle compiling Handlebars templates and you could shoehorn RequireJS into working with Ember, it's definitely much easier to "go with the flow" that Ember on Rails provides. I'll likely write more in detail about this in the future (though don't hold me to that).
I've built Noted to be a useful application, not just an exercise in learning. One of my biggest concerns was that notes are important, whether keeping track of a shopping list or needed to cram for an exam the next day, and that not being able to get to them would be a complete dealbreaker for a service. While I couldn't promise perfect uptime, I could promise two things:
Thus, instead of rolling a custom back-end, I integrated with Dropbox. Not only that, but the Dropbox integration is entirely handled through the client-side with Dropbox's JS library, so that if my server is entirely down, you can still export your notes to Dropbox. Between that and the offline-by-default abilities provided by HTML5's Appcache APIs, after you visit the site once, you basically never need to connect to it again (except for downloading updates).
I'm really proud of Noted. I've been using it myself for several weeks, and I'm glad that this application I've wanted to exist for a year exists and is useable. I hope you consider using it too.