just my 2 cents, and another possible approach
I read what I think was a good book on SEO and URL rewriting, and the method I have used retains the category id and item id in the url but also adds the product/category description in the url
The method uses a couple of functions to rewrite the url dynamically and htaccess.
You can see an example at http://hutchinsonsgardenbuildings.co.uk, (garden buildings).
If you are interested in this approach, I can send you the functions and the htaccess rewrite regex