As with any good xkcd, this one has a serious point behind it. Spambots and other autonomous agents are becoming increasingly sophisticated. There may be a time soon when captchas and Turing tests may be a requirement for any sort of online interaction.
Although it’s a bit moot once bots can convincingly beat a Turing Test (does it really matter if your online buddy is a program if they’re reasonably good chat?) it’s going to really change everything about interacting socially.