My Mrs has a blue badge, can no longer drive and has to use a wheelchair. She can't self propel and relies on me to push it. The rule is simple for me. If she's getting out of the car then I park in a disabled space, if not I use a normal one. We get a lot of filthy looks from the older generation, they seem to think the spaces are for old people, not disabled ones. In most normal parking spaces it's impossible to squeeze a wheelchair between 2 cars, never mind have the car door open fully to get her out. It's a bit of a fiasco in some car parks with me having to move the car in and out of a space to get her out and back in whilst other people are trying to drive around you and park in the space you're still using. Extremely rare we park on double yellows, they are there for a reason so chances are even if entitled to via a blue badge that the car will be causing a problem in some way. What really annoys me are people parking in front of dropped curbs even when there's markings in front of it indicating that it can't be parked in front of! You don't realise how high some curbs are until you're trying to get an adult in a wheelchair up or down one without tipping them out. This is a regular occurrence at our local GP practice. Even the bloody Dr's park there and complaining has no result. Dr needing to park his car trumps disabled access.
Our local tesco has made the mistake of putting a whole row of disabled spaces in front of the cash machines so of course every tom, dick and harry parks in them whilst they go and get money out. What people need to think about is that it's not necessarily the distance from the store that's the issue, it's the physical space that some disabled people require to get in and out of the car.