This is a good supplement if you're interested in the free vs. not-free debate (aka M. Arrington vs. 37signals). The concept of "mental transaction costs" -- the "cost" associated with making a decision of whether something is worth paying for and how much is it worth -- is a useful one. For me personally, if I decide something, particularly an online service, is worth paying for at all, I'd probably just as soon pay $20 as some fraction of a penny. In other words, if it's not free and it's claiming to add value to my life, it had better be adding at least $20 worth and convince me as such. Then again I've never given much thought as to what micropayments would be good for, so counterpoints are welcome.