It's funny that the title of this thread is "The ESFP "stupid" myth," when in reality, the so called "myth" is based after direct observation in the real world.
Let's face it, ESFPs are predisposed to stupidity, and there is no use defending them. They are shallow, linear minded, unoriginal in every way, tasteless, clearly lack abstract reasoning and don't care for it at all (sure sign of somebody with an insufficient critical thinking ability, it just doesn't exist for them!), and are "intelligent" only in the most practical of ways. This is hardly indicative of true intelligence (i.e. NT), and is more suited for somebody who lacks real world perspective (another flaw you can add to their rather lengthy list.) That being said, I find it comical that some of you point out anecdotal evidence of ESFP computer programmers and "intellectuals" (as if, even if some do exist, they're using SF skills to derive the logic required to understand the material! HAH!), when it is clearly contradictory to the facts. Cut the PC nonsense and call a spade a spade.
Just to add contrast to the anecdotal evidence of the pervasiveness of supposedly "smart" ESFPs, I will bring in some anecdotal evidence of my own: I know at least four proven ESFPs (which I have informally managed to test), all of whom are complete and utter morons, who albeit putting up a pretty front, are at the lower end of the thinking chain. Whatever they amount to in life external of social pretense, will never be due to their ESFP skills.
To finish it, I would like to state that this is not intended to be a rant or slander against ESFPs, it is simply the observed truth about the ESFP when it comes to the topic of being stupid. There is also no need to complain about the fact that I may be "overgeneralizing" ESFPs, which is not the case in the least, and while my remarks obviously don't apply to every single ESFP equally, they do apply to the Myer-Briggs archetype of the ESFP, and so their contents naturally manifest themselves in the real world. ESFPs are generally nice and cheerful, and easy to deal with, but intelligence is rarely one of their traits.
I only know one ESFP (male). I asked him to take the MBTI and he tested ESFP. With that said, he is one of the most retarded, non self-aware, tactless, judgmental and cognitively challenged person I know. I laugh at him constantly and I can't bother to argue with him because all he's got is: "that's the way it is", "that's the way it should be", "just 'cause" and "but it's wrong" (with nothing to back it up). He does not listen to facts, reasoning or answer directly to questions about subjects he feels uncomfortable with. He's a total sheep and does whatever everyone else does without thinking it through. He's awkward and stiff, always seeking other peoples approval. Also, he talks shit about people behind their backs, while acting nice and friendly towards them face to face. He's very easy to befriend and to get along with, but there's no depth to him. There's only Level 1. He can also change his mind about some thing quick, without any kind of responsibility to the task at hand. He just doesn't think long range. But, I've known him for years, he's my friend and I have a good time around him. Most of the time. That's just my observation of one ESFP I've known since junior high.
I know a few ESFPs. My current roommate is incredibly smart, she got over 1500 on her SAT and had a 3.8+ at UCB. I still think certain actions she takes are completely idiotic, though
Another guy I know is ESFP and is one of the smartest people I know. He just doesn't really care much about having N style conversations. But he follows everything everyone says, and is much quicker than almost anyone.
Both are very impulsive, though, and are always getting wasted and acting like idiots.
The third ESFP in my extended friend group isn't very smart (although she still got into Berkeley, though that's not necessarily saying much)...and I'm always really annoyed by her. It seems like she doesn't plan anything at all, and never learns from her mistakes.
But yeah...I don't think most types are significantly correlated to intelligence, except maybe IxTxs being predisposed towards thinking more in a way that makes them better on IQ tests. Any statistics anyone can use in response to this can be thrown out as you never really know if people are typed correctly.