Sure, I think there's a big difference between programmers (and similar) and the situation in France at the time, when most people affected by this were factory workers, who didn't have themselves much influence over how productive they were (aside from the obvious issues of not showing up / slacking off).
Basically, "nothing" happened. The expected drop in unemployment never materialized. And although pay rises never were an expected effect of the change (from what I know), they were negatively impacted.
I'm not knowledgeable enough in those matters, so I may be off base, but it would seem that companies started to be less "competitive" when the rule started to be applied, in 2000-2002. But from what I've read on the subject, none of the sides (for and against the measure) can prove that it was undoubtedly a good or a bad thing.
> The way I see it, as programmers we will be far more productive working fewer days per week and just taking more time to relax. If this assumption is accurate you have to do nothing to compensate.
I agree with this. Unfortunately, I'm not in a position to make this kind of decision. And it's pretty clear to me that many managers don't think this way, and somehow figure that your productivity is roughly constant and proportional to the time your butt spends in your seat (at least up to a point).