>And, surprisingly, it does work the other way 'round. Well, almost. Once during the years of the wars in which my country "didn't take part", we went to a peasant's barn to buy some gas for the company Yugo. The barrels weren't marked, and we were very tired (worked all day at the customer's, and had a three hour drive home ahead of us) so nobody noticed which barrel was greasy and which was clean... so we poured from the greasy one. Which meant diesesl - gasoline evaporates and doesn't leave stains. We tilted the Yugo about 20 degrees to the side so we syphoned out most of the diesel, and then poured the regular in. Unfortunately, we did try to start the engine on diesel, and it sucked some of it into the carburetor.
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>And it worked! Though, first kilometer it spewed out thick black smoke, and coughed and hiccuped a lot, until it came to slurp the clean stuff. Then it purred on.

I actually didn't like the idea of the attendant to siphon the fuel out, and was glad the tank design prevented this. In the shop they took out the rear fuel pump and emptied the tank much better than you could with a regular hose, blew the pump, added 15l diesel and some diesel conditioner, and asked me to fill up asap. If you run a diesel engine on gasoline, or a mix that ignites prematurely you could cause a lot more (expensive) damage to the engine, injector, etc. than running gasoline engine on gas-diesel mix. In the past you could run the diesel engine on almost anithing, from used cooking oil to coal dust, but newer injection systems are more picky.
It's nice that you can't fit the thicker diesel nozle in a gasoline tank, but not fair that you can stick the gasoline nozzle into diesels - they should be formated to not allow either one to fit into the wrong tank.