The problem is that they increase in value, to a degree that the individually rational choice is not to spend them "now". The babysitting coop coupons were eff

The problem is that they increase in value, to a degree that the individually rational choice is not to spend them "now". The babysitting coop coupons were effectively subdividable as well: participants could have taken the initiative to say "I'll provide two hours of babysitting for an hour coupon" or "I'll provide 15 minutes of babysitting for 1/2 an hour coupon". [Edit, for elaboration] That would be rational when the value of babysitting in the further future (e.g. Valentine's day) exceeds the value of babysitting in the nearer future (e.g, Feb. 11).