Google's "I'm Feeling Lucky" button - What is it?

One of the most notable objects on the Google Web search is the I'm Feeling Lucky button.

Ordinarily when you type in a key phrase in a Google search, you press the search button, (you can also just press return or enter on your keyboard) and Google returns a results page that shows multiple Web sites matching your search phrase. The I'm Feeling Lucky button skips the search results page and goes directly to the first ranked page for that search phrase.

If you type "white house" in the search box and press I'm Feeling Lucky, you'll go straight to www.whitehouse.gov. If you type "apple" into the search box and press I'm Feeling Lucky, you'll go directly to Apple Computer's Web site.

I'm Feeling Lucky is handy if you're fairly confident that the first result in the search engine is going to be exactly the page you want to find. It saves time and clicking to just go to the page with the first click. Using the I'm Feeling Lucky button is also a common way for people to jokingly point out Google bombs. It adds an element of surprise to the joke.
Mystery Countdown Ticker

As of December 2009, pressing the I'm Feeling Lucky button without putting anything in the search box will yield a countdown ticker. There's no official announcement or explanation for the countdown, but it seems to be a simple New Year's ticker.
Lucky in Other Google Tools

Google Toolbar has an I'm Feeling Lucky search built in, which works the same way as the regular Google search.

Picasa also has an I'm Feeling Lucky button, but in Picasa's case, the button automatically applies enhancement filters and adjustments to an image.