This discussion seems to be solely oriented towards academia...
But, I may add, two career couples can have lots of difficulties
finding jobs in the same city even if they are not in academia!
Particularly today, when the IBMs, the Bell Labs, and all the
other industrial research labs. are cutting back, the pharmaceutical
industry is hesitant waiting to hear the final word on the
health care plan, and government research labs, such as NIH are
cutting back on permanent research positions. I think it is
extremely difficult for two people who are in highly specialized
technical fields to get jobs within the same geographic area,
and it is great if they succeed!