This would have been a better project, and had probably gotten a lot more traction, had it provided plugins for the big editor suites -- eclipse, visual studio, etc. As the project stood, it's neat, but at the same time, it's an impedence mismatch. You can't just annotate in your environment of choice, you have to go into a browser window to view the same code you have open in another window and see if there are any annotations. There's a place for something like it, but it needs to be a lot more intimate with how people already work in order for it to get any sort of needed traction.
Founder here. Yes, this is absolutely true. Problem is, one editor integration doesn't cut it. Or even two. The editor world is balkanized, and even targeting the "most common" tools wasn't enough. Early adopters are probably more varied in their editor use than the general developer population.
More importantly, that was just one feature in a pile of other "must have" features that people said they needed. It was on the roadmap, but we never got around to it.