Bernardo Blum & Avi Goldfarb, Does the internet defy the law of gravity?, Journal of International Economics, 2006:
We show that gravity holds in the case of digital goods consumed over the Internet that have no trading costs. Therefore trade costs cannot fully account for the effects of distance on trade. In particular, we show that Americans are more likely to visit websites from nearby countries, even controlling for language, income, immigrant stock, etc. Furthermore, we show that this effect only holds for taste-dependent digital products, such as music, games, and pornography. For these, a 1% increase in physical distance reduces website visits by 3.25%. For non-taste-dependent products, such as software, distance has no statistical effect.