People who pay lots of money (or their employer's money) to fly to a conference and then sit in the sessions tweeting or surfing the web as though it were a slow day at the office are ultimately just impoverishing their own mind (like the people who don't have the patience to read books or who hate movies that don't do all the thinking for them).

They are only dimly aware of what's going on around them and shut out stimuli which they judge to be "boring" or "irrelevant to me" in favor of their familiar, unchallenging stimuli. It should be embarrassing, but somehow it's socially acceptable to be the equivalent of the guy who shows up to conference without doing the reading because he was playing WoW all night.

I went to RailsConf with a coworker like this and although I like her personally, she spent one of the more interesting sessions reading web comics and remarked "Wow, that was boring" afterwards. Well, yeah, you tuned out in the first 3 minutes.