I can't comment about the use of 'Hyboria' instead of 'Hyborian Age'. So I won't.
But I would say that calling anything "Dungeons of..." in a Conan sourcebook would have the anti D&D and d20 mobs burning their internet torches and sharpening their forum pitchforks in an instant.
As game writers and designers, we can't make everyone happy, unfortunately. No matter how much we'd love to make the perfect product.
Again, I only hope the meat of the book makes up for any teeth gnashing over the title.
Cheers all,
Bry