We're probably all guilty of it at some point - however if I've got cruise control on, then if someone's tailgating me, too bad for them, I ain't changing speed unless it's for safety (and I don't lane-hog btw)I'm very guilty of watching the speedo.
Even if I put cruise control on, someone gets up your back..
And as you say bmw drivers still bomb past regardless, like they are in the Stonecutters and know which ones are live cameras and which ones are blag.