Jared Spool gave a key note on search and e-commerce. There were a number of interesting points he made. In his studies of e-commerce sites, he found that the most successful sites, used search the least. Search is our tool to be used when navigation fails. Improving the "scent" of the links on the main page, or within the navigation hierarchy, will decrease the need to use search.
UIE collects 2000 pieces of data per participant. In their studies they found that the #1 predictor of success was the # of pages the user visited between the home page and the sales cart. Fewer pages led to greater success. The best way to improve scent is to build the trigger words into the link titles, or the description of the tool. To find the trigger words, examine the search logs - those words are the words the users are scanning the pages to find. Referring again to his studies, he found that no one only went to search. Everyone started by scanning the page, looking for categories or links that contained the trigger words. They only went to search when nothing could be found.
An interesting point he made, if you can follow the users click path and know when they leave the page through search, then you can know when the trigger words dried up. Adding a link on that page that takes the user to the search term will increase success for that one trigger word.
Search works well for known item location. So it is easy to find "The Princess Bride" or "Tom Clancy". Search does not work well for less concrete items like "an inexpensive yet high quality SLR" or "Novels written by Nobel Prize for Literature authors". To solve this issue he recommends using editorial capability to improve content finability.
Looking at 77 installed versions of search engines on e-commerce sites, the same vendors that were the best, were also the worst. The difference is the implementation, not the technology. Focus on doing a good job on configuring the installation.