Like most posters I've had doors come open in a number of small types (PA34, PA44, PA28R, various Cessnas) with no issue. By far the biggest risk is distraction. This also applies to malfunctioning door open sensors in Diamonds.
I sometimes fly an aircraft with a sliding canopy. It's certified but not too common. There is an unwritten SOP that for this type, when operating somewhere quiet with nobody else in attendance (to help extract you or call the fire brigade), we take off and land with the canopy fixed open (below about 500ft).
The idea is that if one had a problem and had to land in a rough field or long grass and flipped over, it would be pretty hard to get out unassisted with the canopy closed.
The aircraft also has an "E.E.D" (emergency escape device = Homebase claw hammer) for such purposes. The forced landing and ditching checklists have "canopy fixed open" on them, too.
I guess other types with canopies like Chipmunks and so on are similar?