As a lawyer and entrepreneur, I suppose I ought to weigh in here ;-)
Post-term non-competes are tough to enforce in CA, and generally only used in cases where a shareholder sells all of his/her goodwill and stock to a company, in which case the company can enforce a non-compete for a reasonable time and within reasonable boundaries. Non-compete provisions that are effective during engagement/employment are of course far more enforceable.
NDAs are far easier to enforce, and while there are some limitations, I would never advise anyone to take an NDA lightly.
Beyond the strictly legal aspects, you raise the issue of whether being asked to sign an NDA before having initial conversations with a potential co-founder is a good thing. I've found that those who insist on NDAs before having even high-level discussions are generally more paranoid and/or less seasoned entrepreneurs. I won't sign an NDA just to start initial conversations with potential co-founders, nor do I ask others to sign an NDA in similar circumstances.
Having said that, if one has truly valuable and confidential information, then he/she should be careful about disclosing specifics without an NDA in place. In other words, I normally have high-level discussions sans NDA, and then get an NDA in place before sharing the secret recipe, so to speak.
I deal with NDAs, non-competes and all other co-founder and startup issues all the time - if you ever need help, just email me at email@example.com