I started to write a comment on Profgrrrrl's post about this, but it was getting out of hand!
Because I am one of the very lucky ones, I don't really feel that I can comment in an objective way about this. I am extremely lucky to be in the same department as my husband (H) and we are both tenured (went up at the same time even!) I felt like that was the true test of our 'worth'- could we both get tenure? Yes.
I was hired here first, then H was offered a job later (his record is what got their attention in the first place, but he was put through as a 'diversity hire'). I know we were extremely lucky and there are some people (at our U and in our department) who were not pleased about his hire, but he was a net new line- a faculty line we wouldn't have otherwise. I know it would never happen now given budget cuts, but we came in at a very good time and had a department chair who knew how to schmooze the administrators on our behalf. At the time, H was prepared to stay in his old (tenure-track) job and commute back there for a few days at a time (3 hour drive). It would not have been ideal, but we would have done it and probably kept looking. D was not even three then, so it would have been especially tough for me the days that H was away.
H contributes to the department in significant ways and I often wonder who would be teaching his courses if he hadn't been hired. We don't have any kind of monopoly on department politics (in fact we often feel that nobody listens to anything we say!) We collaborate on research sometimes, alternate teaching one course between us, and I really don't think that our being married has much (if any) bearing on the department at all.
As lucky as we are, it hasn't always been easy. H was shortchanged by the P&T committee one year and forced to forfeit ALL of his years in a TT position- that meant that we went up at the same time. It was stressful to be going through the process at the same time, but also a lot of pressure to not 'blow' our excellent situation. That was why we never talked about having another baby until after tenure (and that didn't work out). I sometimes wish that we had just had another child earlier, but H always reminds me "what if we didn't get tenure?" I tend to think that things would have been fine, but who knows how having another baby would have impacted my pre-tenure productivity.
I think it's hard to make sweeping statements about spousal hiring one way or the other. In some cases they can be good and other times there can be problems. I can understand the resentment from others, but I'm in no position to judge. I'm just very lucky that my U has a favorable attitude about it- they have even created positions (non-TT) for same sex partners. Pretty progressive for Small Town Midwest!