I've done oranges, bananas, and broccoli.
It's actually somewhat common to feed bananas to Copperband Butterflies.
http://www.youtube.com/watch?v=kYv6eBdtAbU
I normally would agree with the little bit doesn't hurt, but two concerns off the top of my head, acidity in some of the fruits, oranges etc. Nothing these fish normally would eat is acidic at all. I imagine it could very well border on burning a fish's stomach, say a large puffer that's used to munching on calcium rich snails/crabs, etc, then takes a chomp out of a orange slice. That straight citric acid could do a number...
The second issue is fiber. Admittedly I don't eat strawberries, but the fiber content may interfere with digestion, and become blocked/impassable for the fish. The cell walls of terrestrial vegetation are super tough compared to aquatic vegetation.
When I feed the broccoli, it was blanched, then frozen. The oranges and banana were froze and thawed twice before feeding to help break down the cell walls.