Let's Talk NDAs

I think that it would be constructive to have a discussion around NDAs.

In the places that I've worked, the NDAs are unbelievably onerous to the point where if you take the writing at face value you can't even disclose fund returns or any discussion of fund strategies. Obviously, they have every incentive to write this as strictly as possible, but what is actually enforceable?

I'm specifically referring to your human capital - the skills and knowledge of strategies that you learned of during your employment.

1) To what extent are you allowed to talk about things you have worked on and market yourself?
2) To what extent are you allowed to replicate processes/types of analysis that you have worked on in the past?
3) What are the potential repercussions (let's completely ignore the things that are obviously illegal and unethical like stealing computer code)
4) Say you ran a profitable equity pairs-trading type arbitrage that you spent all of your time on and don't have a noncompete agreement - to what extent can you run this same arbitrage at another firm?