Well, I think ya'll covered most of it pretty well. I'm with Lux on the use of ngons.

Ngons are a non starter for me, an absolute no go. Too many issues with how they're divided at the time of render [all render engines render in triangles so far as I know, real time or otherwise], whether the engine ends up converting them to stripes or fans, what each of those solutions can do to your shading, and instances where the ngon actually triangulates outside of itself causing light leaks. On top of that not all software will handle/divide them the same way, so an ngon that isn't in issue in one package might be in another. If your mesh doesn't work pretty much universally across software packages, that's sloppy modeling. Those same issues [striping vs fanning/etc] come into play with UV mapping. The only thing you can really do is planar map an ngon, if relaxing the layout causes the ngon to distort even the slightest it can make a mess of your texture.

As far as ngons saving time, I can't really see where it should take more than a minute or two to patch an ngon with quads/tris, unless its massive, in which case you've got potential for all sorts of the mentioned issues to crop up and it should probably have been divided up into smaller chunks at the very least to begin with.

 

No issues with triangles here. Should be avoided in meshes that will be deformed if possible, but so long as they're used sparingly and placed wisely, I've no problem with them even in that case. Non-organic meshes, again no problem with triangles on those, as long as they're placed wisely, flat planes being the best place for them, as they will pinch on curved surfaces if you're not careful [but so too will four point triangles/poles].

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