US Transits
Some great posts here, and in general I agree with most of what has been said. The US has improved significantly in the past couple of years, so that most times, whether in transit or arriving/departing both immigration and security are a fairly painless experience. It still depends a little bit on which airport and which terminal you use. Ben Bradley Intl Terminal at LAX can still be pretty bad (slow lines, many non-English speakers), but T2 (which ANZ uses, is generally pretty civilized). Miami, which I use regularly, and was a hellhole for years, actually won Best Airport award last year and has really cleaned up its act. The last few times I've been through I really couldn't fault it. Nearly all US airports now have dedicated and efficient fast track lines for premium travellers, as well as special lines for families/babies/etc.etc. Many carriers (VS and BA for e.g.) have dedicated premium security channels - BA First at JFK is the best I have ever used.
How is all this done? In one word: consistency. The rules are clear, everyone follows them, and it is done efficiently and courteously.
As someone else pointed out in this thread, compare the US with the abysmal situation at BAA airports. Ferocious, nasty, undereducated pre-screeners who got the job because they failed the traffic warden exam., totally inconsistent and arbitrary application of rules, thuggish lack of courtesy and general chippiness throughout.