Back in 2007 I tried an experiment with some coworkers to see how well other search engines worked. We wanted to know, from experience, how well faceted search, guided navigation, search presentation layers and so on were in day to day life. If you are interested, you can see the entire experience here: http://30daysgooglefree.blogspot.com/. In the end, we determined that if the search engine gives you a good document on your first page of results, you won't need these other search tools. If it does not, then you will not see a great improvement.
I was a bit disappointed, really.