I wanted to expand a bit on the critique of reason as mentioned in my previous post on Rand, and readers should keep in mind that this is chiefly a response to a strain I've picked up on in popular culture which may or may not accurately capture anything Rand actually said (though it does match my 20+ year old recollections of her).
Back at the dawn of the Enlightenment, it made perfect sense for philosophers to stress the role of reason in providing knowledge as opposed to faith or authority. The conflict with faith still exists today in some form, but has been much attenuated, with faith (in academic circles at least) backed into a small corner. Moreover, sophisticated advocates of faith today still explicitly use reason to justify faith itself, i.e. not the content of the beliefs taken on faith, but the act of choosing faith. This defensive move marks the virtual victory of the Enlightenment when it comes to requiring rational justifications for beliefs and actions, i.e. demanding reason.
Calls to use reason are currently synonymous with calls to know thyself, to think about what you're doing, i.e. calls to philosophy in general. To be reasonable is to not be blinded by passions, to not leave your assumptions unchecked, and to subject your and others' arguments to careful critical scrutiny. Granting this starting point, though, one's model of how reason actually works can be more or less naïve. An unbridled enthusiast of reason may see reason as by itself capable of answering all legitimate philosophical questions, and of positively directing, at least for an individual in a particular situation, an overall approach to life and the content of every significant decision. Actually diving into the history of philosophy with some spirit of charity belies this conclusion. Does reason, for instance, entail that we reject all religion? Well, it's a tough call. Probably not. Does reason entail a particular political stance? Well, it certainly seems to rule out quite a few, but it strains credibility to believe that given the numbers of smart, careful thinkers on both the left and right (and perhaps more of them not holding positions that fit on that spectrum) that reason itself rules out one of their positions completely.
Here's the problem: explicit reason is generally good for evaluating the strength of particular arguments and identifying the assumptions that would make them tip one way or the other. However, to then make a overall judgment call about an approach to life as a whole or some significant portion of it in light of numerous arguments, as well as considerations (there will always be some) that you're aware have remained largely unanalyzed, requires that damned Aristotelian practical wisdom (phrónēsis), which is a matter not of explicit reasoning but of overall "reasonableness," which is much less easy to spell out than, say, the rules of deductive logic, and I would argue by its very nature phrónēsis can't be spelled out without an infinite regress, as it's about how to sensibly interpret and apply specific insights. Rules for applying an insight would themselves require sensible application, i.e. rules for the rules, ad infinitum.
My comments above about religion and politics above constitute an inductive argument: we don't actually see, in detail, the life-long workings of (most) other people's philosophical development and self-examination, so in judging, e.g. "all theists are irrational" or "all lefties are sentimentalists," we'd be in essence judging these people by their results: we'd have decided already that there's no reasonable excuse for such a position, so therefore people holding that position must be screwed up, even if I haven't seen first hand the actual flaws in their approach (and of course one can typically interpret other people's behavior to "prove" our prior assumptions about them, e.g. if I think like Nietzsche that Christians are underlyingly bitter, I'll read all sorts of repressed rage into their behavior). The alternative, which I recommend, is using the principle of charity: From what I've seen, plenty of smart, extremely reflective people, linguistically competent and with full access to the history of philosophy and logic, have held these positions, so let's just grant that they're not self-deluding. That doesn't mean that I won't pull out my best critical faculties when arguing some particular point with them, but it does mean that I don't go around declaring people that think like I do as the only reasonable ones on the planet.
Insofar as objectivists, or the scientism-striken, or especially enthusiastic Enlightenment-era authors, or anyone else holds up reason as an excuse for some form of dogmatism, then they are not being reasonable at all. There is no shortcut to actually engaging the troublesome problems of philosophy, no principle of verification or behaviorist linguistic stipulations or even a thoroughgoing empiricism that will effectively enable one to lop off in a couple of swipes the dangling braids of Being, Existenz, the limits of space and time, the origin of the universe, free will, mind-body, and the rest of the historical menagerie. Certainly the uninformative proclamation to simply "be reasonable" won't do the trick, as if philosophers hadn't been already trying to do just that pretty much since Plato.
Image note: this inexplicable image came from the My First Dictionary blog.