Is there anything wrong with discussing a project with colleagues or family if confidential information is not part of the conversation? What if you limit your discussion to only information that is already public (i.e., it has appeared in company press releases or published interviews)?
There is some logic to your question - what could be wrong with divulging already public information? After all, most consulting agreement clauses relating to proprietary data relieve a consultant from liability when the information revealed was already in the public domain. So, what's the problem with discussing information about a project with friends and family that anyone could easily find in the newspaper or from a company public official?
As logical as this might seem and as consistent with the contractual agreement of proprietary data as it is, discussing such information is simply not your call. You have an obligation to keep such information confidential unless directed by your client to discuss it publicly. This is a matter of professionalism, not legal compliance. Just because you are allowed to discuss it doesn't mean you should. Your client depends on your discretion to keep project information safe and not discuss it with others. There is no reason to discuss your project unless it is of direct benefit to your client, and then you should be coordinating directly with your client as to the timing and content of such disclosures. Some clients do not permit even disclosing that you are working for them or the nature of your project. You won't know how sensitive some information is until you ask. Information from an "inside source" (you) may give a different impression than when it comes from a press release.
Tip: This is a topic your client will appreciate your bringing up. Explain that you would like to discuss non-sensitive issues with your professional colleagues, perhaps to provide additional insight into the issues and perhaps to help them understand your skills better. Whether or not such discussions are for your client's benefit, get explicit permission before you hold those discussions.