As someone who teaches many web search training classes I would like to offer a tip o' the cap to a simple but elegant feature found on AOL's advanced search page.
A frequent challenge to new and even some veteran users of advanced search interfaces is entering terms into the various boxes and then not having a clear understanding (aka confusion) of what they are or aren't searching.
AOL's Search Preview, located on the right side of the advanced search page, takes the material entered into each search box and uses it to dynamically generate the query into a single easy/easier to understand sentence. Words and items that will be searched appear in green. Material that will not be searched appears in red.