In routine application development (which, to be fair, is a slightly different problem than a kernel,) TODO comments are probably at their best when identifying

In routine application development (which, to be fair, is a slightly different problem than a kernel,) TODO comments are probably at their best when identifying code deficiencies that you don't actually have plans to fix, pointing out refactoring opportunities, and documenting other hacks. If you put this sort of a thing in a bug tracker or other system, no one will see it when they browse the code. (On the other hand, the bug tracking system is definitely the place to put things which should actually get done.)