The more I hear, the more I think that it is the luck of the draw with who you get as the IO. I don't know about you but I size them up when I am in line hoping that I will get the one that looks "nice" (if you can even really tell).
The only time I got more than a few questions was last time going through Heathrow where I got an IO that was clearly not British born. Perhaps they have something more to prove or perhaps it's a cultural thing. I hate to go down those lines personally....
As for the US border points, both going and coming, I find them to be mostly on a power trip. I am always courteous and never have an attitude of annoyance. IF anything it's more of an attitude of relief. When I am leaving LAX to visit my sweetheart, I am more than happy to be getting on a plane. When I return to LAX, although being separated is hard, I am honestly glad to be home again!
I know for a fact that being jet lagged and slow in responding does not do the Brit well coming through immigration. I think the IO's can take advantage of that.
And speaking of immigration, I will be leaving the UK on Sunday back to LA. This time I put my COLEMANS mustard in my checked in suitcase and NOT my carryon!! That did not go over well last time!