@matigo The type-shifting fields are a bit of a pain to work with (false or totally-not-a-Boolean). But I've clearly been able to cope. ;)
The main thing that gets me is not knowing the full range of possible data "shapes" and what each means. The smallest example is enumerations, but the "hidden post oops" was another case of that: it turned out posts could come down looking different than anything I'd seen before or knew to expect.
One thing that kind of surprised me is that posts don't have a links like mentions or hashtags that list out the links. You have to scan those out of the HTML or Markdown manually. (Profile descriptions ended up being very post-like in ways I'm not doing anything with yet, either.)