I went live last night. I'm still trying to make up my mind on how I feel. I don't think it will ever be a "google killer" (sorry for the cliché), but it is quirky and cool. However, it keeps timing out on my search tests, so I haven't been able to do a thorough investigation.
Also, here's an MIT Technology Review article on how Google and Wolfram Alpha match up, and a neat article from the Wolfram Alpha blog on how the "computational knowledge engine" interacts with Mathmatica.