Black patches are a result of having AO set improperly... that's a user issue.
Most other applications (including lightwave) recommend NOT using double sided polys, because they create rendering issues.. again, it's a matter of end users not creating properly.

I'm an end user.. I made BOTH mistakes (sometimes NUMEROUS times.. LOL!) I learned my lessons though.

Lightwave's "merge polys" is my freind!

Way too many people take way too many things way too seriously.