[zdragnar]

An appropriate limit is, as I mentioned, editorializing. To be precise, your clients, peers and users should not the the target of your feelings expressed in comments.

An additional litmus should be professional discipline: express dissatisfaction with a todo (ideally referencing a bug or discussion issue source URL or identifier). Without that reference, it acknowledges an issue without indicating any motivation to solve or re-mediate the original cause, which is (IMHO) indicative of a careless and lazy attitude.