Glen has an interesting post examining the most recent Matrix flick in light of Robert Nozick’s famous “experience machine” argument. While I do think Nozick’s argument is a powerful intuition pump (I use the phrase in a non-pejorative sense) exposing one problem with utilitarianism, I have never held that there’s anything necessarily irrational about hooking up to such machines. In fact, I can think of two main reasons you wouldn’t, only one of which applies to the Matrix of the films.
One is that you’ve made a search for truth—the scientific quest to uncover the deeper structure of reality, say—part of your life’s mission. You could realize this to some extent assuming that the Matrix were programmed to be isomorphic to the external world in the appropriate ways, but you’d learn no more than the programmers were able to encode, unless the Matrix were somehow hooked into telemetry that allowed you to further test certain properties of the real world from within the Matrix, which would make it more like a kind of interface with reality (an alternative to your natural sensory apparatus) than a really separate reality.
The second, and more universally human reason not to hook up to a Nozick-style experience machine, is that you care about other people. You don’t want the experience of having loving noises and facial expressions made in your direction; you want love—a genuine connection with another human mind. You might want this (I’d argue most of us do want this) even if the simulation were subjectively indistinguishable from the real thing. But the Matrix is not a one-person affair, as Nozick’s was. You can fall in love with another real person there, just as (or more easily than) people can really fall in love online. So the case against hooking into the Matrix (assuming sufficiently benign machine overlords) is really much more narrow than the case against plugging into Nozick’s machine.