What are good Gray Hat Techniques?

What are good Gray Hat Techniques for an established site?

It's ALL "grey hat", AFAIK. Buy a single backlink and you've "crossed the line". Google doesn't see "greyhat", it's one or the other. We call it greyhat because there's a difference between breaking Google's rules because everyone else is doing it and you'll be at a competitive disadvantage if you don't, and breaking Google's rules in ways most people do not know about and possibly even Google cannot anticipate.

There's driving 70 mph in a 65 mph zone in order to keep up traffic, and there's driving 90 mph, risking your life, running others off the road and inviting the Police to put you in jail.

Heh. Good Metaphor, Nigel.

So, what's your definition of "greyhat" techniques? Some people think it's wrong to even be on this forum.

Is Web 2.0 Links considered grey hat? Where you'd added a page with links to money site, then get a lot of links to that said web 2.0 page?

What about .edu and .gov linking?

Any kind of artificial link creation is considered against the rules and therefore "blackhat". Google wants "natural", meaning that you as a marketer do not go out of your way to create the illusion of popularity.