My favorite feature? When you highlight a word on any page a drop down menu automatically appears (see image below) that lets you:
search for the highlighted words on the web with any of four search engines
search for highlighted terms in four social bookmarking systems
do a blog search for highlighted terms
search for your terms in the entire site you are on (Google, Yahoo, Ask site: search)
search for inbound links to the URL you are on in four different search engines (including Technorati and Google)
search for your highlighted terms in seven different verticals from local to TV to stocks.