my recent experiences....
tues - IOM-LGW flight cancelled due to the inbound aircraft (LGW-IOM) being unable to land due to poor visibility. fair enough, however the metar stated the visibility would improve to 10km or more. the inbound plane circled the airport for 10 minutes and returned to LGW. 30 minutes later, visibility had improved exactly as forecast.
thurs - BSL-LTN - they had taken reservations for an A320 operation however a A319 turned up on stand. Swissport asked for volunteers to offload and get invol denied boarding. next flight offered was Friday morning out of GVA. i offered to offload if they would put me on an alternative carrier to LGW (since I had planned to take the train from LTN to LGW). They refused to put me on an alternative carrier, only easyjet, therefore I travelled and some people who did not volunteer were invol denied boarding. besides a handful of volunteers, the remaining passengers who were denied boarding were those in rows 27 -31. some of those seated in 27-31 got onboard due to the volunteers coming from other seats.