DUB - screening of shoes is random. I tend to wear rubber soled wedge boots or my trusty FitFlop Billows and usually am left alone... until 2 weeks ago! When I asked the Charm Queen, she said that they target something like 1 in 10 for shoe inspection.
STN - random again. Neither myself or the Husband were asked to take 'em off.
LGW (South) - appears to be mandatory in secondary shoe-only xray machine. Nobody loves this