Searching the web for planes in the sky
If you search Wolfram Alpha for "planes overhead", it returns a list of planes passing over your current location along with a sky map of where to look.
WolframAlpha launches
If you're skeptical of WolframAlpha (as I was), you should watch this introduction by Stephen Wolfram. The comparison to Google (usually "is WolframAlpha a Google killer?") is not a good one but the new service could learn a little something from the reigning champion: hide the math. One of the geniuses of Google is that it took simple input and gave simple output with a whole lot of complexity in between that no one saw and few people cared about. Plus the underlying premise of the complex computation was simplified, branded (PageRank!), and became a value proposition for Google: here's what the web itself thinks is important about your query.