I don't tend to get upset when folks interrupt - most do apologize for intruding - but most are curious about the eReader I'm using and just want to know about it. People tend to want real-world opinion (no matter how biased it may be) from a user. And I'm sure if you expressed to them that you'll only be able to answer a few questions, but that you'd like to get back on track with your reading they shouldn't take offense.
Or maybe just wearing a t-shirt of Tony Montana with the text "I whacked the last guy that interrupted me." may discourage would-be intruders.
