Writing Letters of Recommendation

I'm not sure what I want to say here except (a) writing a letter of recommendation for a kick-ass student is a great pleasure and (b) writing a letter of recommendation for a less-than-stellar student is a pain in the ass. I have written both varieties this week (for grad students who are in the process of applying for jobs). But even the kick-ass student isn't truly ready to be on the market (she's drafted less than half her diss and in all likelihood will not be able to defend by spring, which is what she's claiming in her job letter). And the other three letters I'm working on...well, those are students I have colleagues who refuse to write for. And I don't. Because I'm a female academic. Because I'm a softy. Because I'm untenured and don't want to go against their chairs, who are giving them bad advice (or no advice at all?). The whole process has left me largely frustrated and feeling vaguely like these students have wasted my time because of the futility of the exercise. And then I feel like it's not my job to teach them that lesson--after all, I agreed to write the letters, even as I expressed concern about them not being ready. In a few weeks/months, when they don't get any requests for writing samples or MLA interviews, well, maybe they'll see what I meant.