As described in this posting, it's ridiculously vague, and as I said above, I'd like to see someone try to enforce it. What if I want to mow my lawn on Friday? Is that acceptable? What if I want to mow someone else's lawn as a favor? What if I want to mow someone else's lawn and they pay me even though I'm not running a lawn-mowing business? What if, instead of mowing someone's lawn I help them out by reinstalling some software or configuring their home network? What if I do a good enough job that they recommend me to a mutual acquaintance? To someone they know from their work? To others in the neighborhood? There's a huge range of options that this paints over, and the devil's in the details. As they've described their policy of "giving back" Friday, it could be interpreted as not letting their employees do anything except lay in bed because, damnit, they need to know their employees are resting like the owners intended.
Frankly, I'm not convinced you're seeing the implications to such a vague policy.
And frankly, I think you're missing the atmosphere in which the policy is offered. I think the kind of place that is willing to offer you a 32 hour week with a day off is the kind of place that's not going to be overly concerned about slicing and dicing the policy to the finest point.
It strikes me that a place this good-natured wouldn't split hairs.
Frankly, I'm not convinced you're seeing the implications to such a vague policy.