I am posting because I see some people have commented in 2015. The question is still valid and the answer is "if a dive operator will take the card it is still valid." The posts saying SSI will give you a replacement card are no longer valid.
My wife has a NASDS certification from May 1973. Most of the places we go accept it because they know us. However, I always check. Last year I sent SSI an email to find if they would replace my card. They would not do that directly, and referred me to a local dive shop that had an SSI instructor. He insisted on a check out of some sort and a payment of $200-250 (can't remember exactly).
To me, this is certainly unethical, if not illegal. At least it is actionable if enough people sued SSI. Not much chance of that happening, of course. The reason is that when SSI and NASDS merged SSI became the corporate entity. As such, they assumed the assets, liabilities and obligations of NASDS. NASDS awarded these certifications after being paid for them under the understanding that they were "for life." As any diving reader knows, that is the accepted industry practice. Now SSI will not recognize the NASDS certification without further payment of money for something that was already paid for. I would not mind a small service fee for a replacement card, but to demand another substantive payment is an unacceptable ripoff.
Now, when we go somewhere we have not been before, I check ahead of time to see if they recognize NASDS. Usually the answer is yes. However, I just ran into a PADI operation in the Caribbean that initially said no unless we "upgraded" to SSI. After a few emails, they checked with PADI and got the response that PADI still recognizes NASDS, but has interpreted some of its old certifications as being something less than a basic open water certification. Not sure how they made that distinction because I recall the old NASDS (pre 1973) certifications were a hell of a lot more stringient that a new diver gets under the PADI program.
P.S. We still have her old card with the microfilm training history.