'Well above 500' is probably sensible for modern types unless you need to go lower for a reason.
Apart from the fun factor, it's possible some of the desire to go lower is a hangover from older days, eg. when I learnt on Hueys you didn't want to spend too long up high in case of a loss of transmission oil pressure, in which case you'd be stuffed if you didn't get it on the ground ASAP, and also flying for range was a case of go low and pull about 80% of available torque (about 40 psi out of an available 50 rings a bell unless the brain cells are going faster than I thought) while 'beeping' down the rpm a bit to the apparently most efficient setting, 6400 N2. So going lower made sense in many cases.
To answer your question, flagrant rule breaking is probably high on the list unless they're filming, crop spraying or otherwise engaged in legal low flying.
Increasingly common? Dunno about that, it's all too easy to be caught on someone's iphone video, put up on the web and prosecuted over here, so I'd say people are a bit more cautious about doing silly stuff these days.