"This kind of information will appear in Suggest either above or below the suggested search terms for a variety of queries. For example, you can type "delta 140" to see the flight status. You can also quickly discover the current time, figure out how many Euros you'll get per dollar, or even brush up on metric conversions," explains Google.
My only issue is that Google's answers can't be copied. If you try to select the suggestion, you'll notice that the answer is not added to the search box, so the only way to copy the result is to open the search results page.
Some of the instant answers are available even if you don't use Google's homepage: check the search suggestions from Firefox, Chrome, IE 8 and Google Toolbar.