wyrmio,
I think that Gasax makes a very valid point. Whether you use 100LL or mogas in your 80/87 engine, it's still a compromise, and you are not using the proper fuel for which the engine was designed.
I would never use mogas without a proper STC, but see no problem whatsoever in using it with an STC in place. Every STC is backed up by extensive testing; they don't just hand them out for the asking.
It's quite true that the engine manufacturers discourage the use of mogas. Given their exposure to potential litigation (whether or not they actually have any liability), that's hardly surprising. If they thought that the could get away with it, they would tell you not to use avgas, either ("warning: engine is not designed or intended for actual use")!
It is interesting to note that the FAA has expressly confirmed that (with an STC), mogas is quite safe to use: see
http://autofuelstc.com/pa/faa.html
Ultimately, the only truly objective fact regarding aviation use of mogas is that the cost is significantly less than using avgas. Everything else is pretty subjective, with arguments both for and against.
MLS-12D
P.S. Here is an FAQ that may be of some interest:
http://www.ercoupers.com/service/mogas.html#5. See also Transport Canada's document TP10737, available on-line at
http://www.tc.gc.ca/CivilAviation/ce...ants/mogas.htm