The problems posted in the article are really hard to judge because the author doesn't actually explain what happened.
In the first example, he doesn't try. Fair enough, it's a judgement call on whether to spend time understanding what happened. Personally, I would consider it high priority, because otherwise you have no assurance that the same problem isn't biting you elsewhere.
In the second, he says something that doesn't actually make sense: "Ember's set function has special behavior for values in the content field". I know Ember's source about as a well as anybody not in the core team, and that statement isn't even false. If I had to guess, I'd assume he's really saying something about how ObjectControllers behave as proxies for models.
I don't mean to write off whatever problems he encoutered -- they are clearly real problems, either bugs in Ember or failures of developer ergonomics. If he could point to the specific actual problems I would personally work on a patch to address them. But I don't have enough to go on.