Maybe it is because it is so new, but I was unable to get any results at all for four out of five searches I did using this new search engine. I used some terms for things I'm working on right now that are pretty common and for which I found very relevant results using google.com. Again, perhaps it is still out there indexing the web sufficiently enough to give regular results for things, but I doubt people will adopt this as a tool if they get the same results I did.
Link: Ex-Googler, husband launch new Cuil search engine.
Cuil said its search engine goes beyond traditional approaches by analyzing the context of each page and the concepts behind each query so it can provide better rankings by content rather than popularity.