Point 3 is phrased well in the title, but I'm kind of annoyed at the implication that you should intentionally obscure your URLs. I can see why he makes that point, and I see the benefit, but I also like URLs that make sense when I'm cutting and pasting.
I have a much easier time finding a cut-and-paste error from email in http://bob.com/posts/37/comments/79 than in http://bob.com/postthing/1f724c302a3b69ef9327313adb269a8d, even if the latter is convenient when the site later restructures things or adds a server.