cool Exalead feature

I'm preparing for a whole bunch of presentations over the next few months, so I'm spending more time digging around in the various search engines.

I finally discovered the OPT feature in Exalead. Don't know how I missed it before. The search syntax is:
first-word OPT second-word
and it translates the search to:
first-word is mandatory, and rank ones that also contain second-word higher

I've known that Live.com supports this (first-word prefer:second-word) but, as far as I know, they're the only two major search engines that do.