[totaltec]

Tony,
I appreciate the point you have here. How to cover all the bases, and it looks tricky.

From an SEO perspective, we know Google does not want duplicate content. The same content accessible from different URLs. Canonical tag helps but I am not sure that it is as powerful as removing alternate URLs.

Personally I would want one URL per product. As we know everyone will have a different opinion.

So, why don't we give them options. 3 options:
1. Always redirect to canonical URL. (In this case URL will be main category) This is a checkbox.

If this option is not checked, we present the other two options:
1. Use category based URLS for products. (i.e. Wines/Chianti and Italy/Toscana/Chianti)
2. Use dynamic categoryid in URL ( chianti.html?categoryid=12 )
This is a select box or radio.

I still maintain that the best structure for SEO is mydomain.com/Wines/Chianti.html, but I would not want the product to also be accessible from mydomain.com/Italy/Toscana/Chianti.html

So I would choose the first option I described above.