yes, the line between what is acceptable and what is not acceptable keeps moving (becoming more grey?).

“a rose by any other name would smell as sweet”
-(Romeo & Juliet)

this passage, as you so kindly pointed out, is very appropriate in the world of search engine marketing today.

cheers!

I am not sure on selling links. It is more of a grey area that some search engines frown upon but could hit legal problems from a competition standpoint if they ever took effective measures, and others in the top 3 monetise quite happily.

Doorway pages and linkfarms – that is a blog network by another name, unless they are created with junk.

We live in a world of syndicated content, yet for some reason duplicate content is frowned upon.

The underlying theme is do things that are good for users to find the information they want to find.