Cameron should've found out what was said in the speech.
I used to be a fervent supporter of limited, democratic international government, and I remain a much more jaded supporter of same. We'll get there in a century or so barring the Singularity, but we just hit a snag with Brexit.
William's got a good post on it, as does most anyone with a brain outside of Britain and nearly half the people inside it. I'll add to his points that the situation reminds me a little of the runup to the Iraq War, where the entire rest of the world said "WTF?" to us Americans (partly excepting the Brits) and that made virtually no difference to our politics.
I also agree with him that immediate economic repercussions will likely be somewhat limited. Regardless, we'll need a few more days to see what the short-term impact will really be. Medium-term it depends on what the Leave campaigners and the EU seem to be aiming at - if it's a Norway-style, you obey all the rules but have no control and that somehow feels good outcome, then the economic impact could stay limited. If they want to take actual economic control of their borders, then they're in for serious problems.
Mostly in agreement with William about the stupidity of EU leaders threatening to punish Britain. I think they're not taking the long-term view - if the election had been held ten years from now, the Remain side would've won - and maybe it will, if you don't go out of your way to alienate them. (My idle speculation, btw, is that Cameron is stalling to October in case the economy or something else gives him a chance for a redo election.) Where I'd disagree somewhat is that EU's primary job during the split is to look out for their side. They shouldn't go out of their way to punish Britain, but protecting Britain's interest is the task of the British negotiators.
Interesting article here on Greenland's exit from the EU thirty years ago - it took them 3 years of contentious negotiations to get this island of 60k people out, and now some people there want back in. Have fun, everybody.
Finally, various people like Kevin Drum have said stop blaming the economy, that there's an obvious xenophobic and racist component in significant parts of the support for both Brexit and Trump. That just sends us to the next question though - why are they happening now. In America at least, I doubt our racism is stronger now, certainly not stronger than 20 years ago. So there is more to it - maybe just an accident of political conditions, or maybe something more is happening.