Few things annoy me as much as poor e-mail interactions with companies I either purchase from or am thinking of purchasing from. I am sick and tired of companies who send me an auto-response e-mail and then never follow through with the promised e-mail.
Generally, the situation is improving but it is still far from perfect and there is a long way to go before online customer service gets to the point where I would call it great. One of the reasons Amazon does so well is that they have really focused on customer service and it shows.
I am told this law has some applications in other fields as well.