The job summary calls for a project manager to work on "a search platform supporting hundreds of millions of users" and "play a part in revolutionizing how people use their computers and mobile devices." That could mean any number of things, but let's play a guessing game.
Assuming that Apple really is building a search engine, chances are it's not likely to be a direct attack on Google -- no one is going to switch their search engine to applesearch.com, and Apple knows that. Instead, any search effort is far more likely to be baked into Siri, Safari and Spotlight, i.e. places where most won't dig through the options and change their search engine.
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An Apple search engine, as crazy as it sounds, could have a big impact on Google in the long run.Of course, we need to temper this speculation with the fact that no one knows exactly what Apple Search is. It could just be a refined Spotlight device search, a better way to search for Apps or music on iTunes or even an internal tool written up by an over-zealous recruiter (the word "revolutionize" appears in no less than 43 Apple job ads right now). But, with over a billion iOS devices out in the wild, responsible for a lot of searches, a search engine would be an easy way for Apple to pitch a tent in Google's backyard.
Stay tune to GizBot for more updates!