Ex-Google employees unveil a new search engine today out to challenge their former employer: Cuil, pronounced “cool,” launches with 120 billion web pages in its index. My initial tests show that Cuil’s results aren’t quite as impressive as the size of the index, but they’re pretty good. From Cuil’s scant black homepage, enter your query (and it will offer suggestions as you type) and go. A search for Lifehacker yields decent results (though with bizarre images) and an “Explore by category” module on the upper right, which offers related searches. This category list is perhaps the biggest indicator of Cuil’s smarts; for Lifehacker it offers searches for Gawker Media (our publisher), Blogs, Google Services, American bloggers—all spot-on—and one miss, Video Game magazine. (On the other hand, searching for Lifehacker Australia produced precisely zip — no regional smarts here, it seems.) Give Cuil a whirl with terms you already know something about. How are the results? Think Google’s got something to worry about? Let us know in the comments.