As previously explained, as site search function is a must for any e-commerce website as it allows users to find what they’re looking for. However it is not unusual to be flooded by a huge number of search results in such an instance, so an option to narrow the criteria of a search is a very useful tool. If you searched for ‘Lord of the Rings: Return of the king’, you’ll no doubt be given results from CD, DVD and Video Games which match the search keywords. Narrowing it to a search within ‘CD’ would ensure only the soundtrack would appear from the search.

I think Zavvi has it right. It’s not too complicated either. You don’t want a hug list of categories to navigate through, just the main ones which will really help in narrowing down your search.