For decades remote capturing of the data (first from people or TV set talking, then from the working computer) was an effective way for political and business espionage. We saw methods to capture sounds, CRT emission, keyboard clicks etc. Tablets and low-power notebooks give much less information to outside world, yet the spies don't calm down and try to capture even tiny bits of electronic emissions hoping to grab your passwords or even more valuable information.
Though I am a bit skeptical about real-world use of these attacks, you still need to be careful when working with confidential information in public. It is also important to mention that rubber-hose cryptanalysis remains effective and if you have logged into your banking account and the attacker knows that you have a fortune in the bank, it makes sense for him to just grab your notebook and run.