While you might think the whole point of ditching traditional paperbacks and moving to ebooks is to avoid added weight, it's technically true that the more books you download, the heavier your Kindle or other ebook reader will weigh. Not that you'll notice it, since each ebook weighs about as much as a single molecule of DNA.
Professor of Computer Science at the University of California, Prof John Kubiatowicz, explained earlier this week that electrons in a memory device are normally able to float around by themselves.
But when those memory modules are required to store something, they are forced to stay in place - which requires energy. Not much, mind you; around a billionth of a microjoule per bit of data.
Using Einstein's E-mc^2 equation, Prof Kubiatowicz hypothesised that filling up your 4GB Kindle would add around a billionth of a billionth of a gram to the device's overall weight, while the equivalent number of traditional books would weigh in at several tonnes.
It's interesting to note, though, that weight is not entirely eliminated from consideration just because the information is now digital.
Other professors have weighed in on this topic, with Graeme Ackland of Edinburgh University, attempting to pass along a message: "If Prof Kubiatowicz is really struggling with the extra weight, he is welcome to come to Edinburgh where it's cooler, and the lack of thermal energy in his Kindle will more than compensate."