Apparently you don't really work half time even if you're technically in a half time position. You end up working closer to full time. Faculty job responsibilities are not really conducive to being split -- aside from teaching a set number of classes or being on a set number of committees, they are often self-inflicted, so to speak. However it would still be more flexible than two separate jobs for a couple with young children. My understanding is that sometimes the single position can be negotiated up to 1 1/2 if the dean likes the idea.
As Rachael points out, tenure criteria can pose problems for this setup since each person is basically evaluated independently on the same criteria as a full-time faculty member. No one likes the idea of half the couple getting tenure and the other half not getting it, so only people who are both viewed as strong candidates are likely to be successful.
There are some other what-if scenarios as well. For example, what if the couple gets a divorce, or half the couple wants to quit and the other half wants to stay? That could leave the department in a rather difficult situation.
Also, you can't really split a faculty meeting vote, so each person typically gets one vote. In a smaller department this can lead to concern that the two will always vote together and will be able to force their way on contested issues. So the two people have to make it clear that they have their own identities and they have to be trusted to play fair.
The advantage for a department is that it gets two faculty members for the price of one, with expertise in different specialties -- this is especially valuable for smaller schools. It also gets the department some faculty members who have a particularly strong investment and who may be less willing to shop around for other positions. And because it is an attractive solution to the two-body problem, it can lure in candidates who would otherwise go someplace more prestigious.
My overall impression was that you had to find a department and chair who were open to the idea, and you had to approach them with the idea very early on and then tailor a joint application.
-Leslie Baker
I am curious if anyone has heard of two half-time people sharing a tenure-track position? I once worked for a city government agency in which there were 2 city attorneys (both mothers) that each worked half-time to fill a full-time position. Seems like that could be accomodated at the university level.
Also, a quick comment - when I was in graduate school (before my pregnancy), a group of faculty held a discussion group with the students about balancing family life and career. I asked one of the mothers if she felt that she lost motivation for her career after having a child. She said that her motivation actually increased. It was only after I had a child that I understood what she meant. When you are away from your child, you make every minute count.
Beth