Sometimes tech journalists will call a new service a Google killer even when it's not a search engine. That's the case with Wolfram|Alpha. It's easy to confuse Wolfram|Alpha with a search engine. It has a field into which you type a query and it searches its database for answers. But that's where the similarity ends.
Search engines provide users links to Web sites that presumably hold information the user wants. Wolfram|Alpha consults an enormous database to bring data directly to the user. You won't receive a list of links when you execute a query on Wolfram|Alpha. Instead, you'll be greeted with charts and graphs populated with data related to the keywords you entered.
This makes Wolfram|Alpha a very powerful research tool. Wolfram|Alpha employees vet all the information included in the database. They pull data from established and accepted resources. You can use Wolfram|Alpha to compare two subjects within the same category. Want to see if a Big Mac is healthier than a Whopper? Use Wolfram|Alpha to compare the nutritional information.
Because Wolfram|Alpha pulls back data rather than links, it's not in direct competition with Google. You should use Wolfram|Alpha if you need to know information about a specific concept. You should use Google if you want to read the latest news on the subject, find a product review or just browse.