Going to individual academic institutions may be one way, but this would also be quite localized, and hard to scale. It also misses intelligent people who are unable to afford to attend such an institution, especially in a place like the United States where the cost can be prohibitive for many, even with scholarships and other aide.
Reddit probably isn't a good place. There's more snobbery and faux intellectualism there than there is actual intelligence, and that's even when focusing on the more intelligent subreddits. It's similar for those who regularly contribute to Wikipedia. It's more about politics there than it is about intelligence.
Digg is pretty much dead. Slashdot is nearly dead. HN has a rather limited audience. A lot of intelligent people voluntarily choose not to use Facebook, Google+, Twitter, or other social networks due to privacy concerns.
So 4chan does look like a reasonable alternative. There's a large audience, its members are probably smarter on average than you'd find elsewhere, and it avoids many of the problems with the other websites or social networks that put a lot of focus on identity.
More than that, 4chan is a source upstream of other communities you mentioned. Content gets filtered and sifted, and some gets passed on. For example, Rickrolling
became a major phenomenon that way.
I'm going to go way out on a limb here but also I would think that 4chan would be more likely to contain the type of smart person willing to put in many hours into a problem with very little real expectation of an end goal/reward. At least more so than the other communities.
With correct targeting you can get some very smart people.
Sturgeon's Law (90% of everything is shit) applies, and since /b/ is so rapid there is a lot of stuff in that 90%.
When /r9k/ started (I remember it when the Robot image was up) it was interesting. There are a couple of smart people in /g/ (especially if you're interested in Plan9 or FDE under Linux to protect Loli)
There is a bit of a problem with semi-smart people thinking they are smarter than they are. (And because of the volume of people you tend to meet a lot of them).
I do. I've spent a grand total of about five minutes on 4chan, so maybe I've missed the good bits, but it strikes me as utter garbage. I expect they're looking for highly intelligent individuals of a certain kind.
Speaking as someone with minimal 4chan experience, /b/ is probably not "the good bits," but is only a subset of the rest of the site. There is often good discussion on music and movies, for instance.
Dissemination I suppose. 4chan may be a cesspool of sorts, but that cesspool happens to be the fertilizer for a large part of the internet. 4chan is where memes are made.
