In today's economy, with lack of work or job loss, it makes sense.
The stay-at-home-parent, whether its the dad or the mom, needs to realize that there's more to it than just parenting. There are other things that the working parent shouldn't have to worry about, since they are at work all day.
The stay-at-home parent should take on bill paying, laundry, house-cleaning, yard work, scheduling and keeping doctor appointments, grocery shopping, and meal planning with preparation.
In this day and age, it seems like role-reversal when the man stays home. Role-reversal is fine, if the man takes on the enire role. All too often, the man in this situation starts behaving like a baby-sitter. The working mom ends up working and taking care of everything else too, and then when the mom gets home from work, he's done, like a baby-sitter, so she has to take care of the kids too.
As long as you both agree on your roles and responsibilities, why not?