My personal opinion is that ISO9000 registration means very little except that the company is ISO9000 registered. It does not imply good quality. It does not imply on-time delivery. It does not imply much.
When a consumer uses a certified supplier he/she has assurance that the supplier is committed to continually improving product and services and the systems of delivering them.
I do not for a minute believe this is necessarily true. For some companies this is true. For many it is not. I have worked with many clients which ISO9000 did little for - they didn't need ISO to design and manufacture excellent products. They had good communication and business systems to begin with.
In addition, I hear complaints somewhat regularly which amount to: "Such and such a company is ISO9000 registered, but they keep shipping me trash. Who can I complain to? I thought ISO companies couldn't do this..."
ISO9000 is only 1 of many criteria I would consider in choosing suppliers.
This is not to say that ISO9000 registration is useless. Quite the opposite. I think for many companies it is a positive tool. I believe it is a good idea. But I also see other tools which I believe are potentially just as important.
I believe that each company has a 'karma' - a personality. Aspects such as "continually improving product" are a function of these - not ISO9000. While the year 2000 revision is supposed to stress continuous improvement and customer satisfaction more than the '94 version, I think the basic fact is that companies which do not improve are destined to failure by the market.
There are many tools a company can use to improve. ISO9000 is just 1 of the many.