Valleywag reported last week that Google's "I'm Feeling Lucky" button, which takes the user directly to the #1 result for a particular search phrase, costs the company $110 million per year in lost revenues because the button bypasses all sponsored results (and is used in 1% of all searches).
Ironically, people still don't know what it is. I remember thinking that "I'm Feeling Lucky" would randomly bring me to a website related to the search term, but it didn't necessarily have to be the #1 ranking.
Why does Google keep it? It's part of who they are.
A few years ago back at SES NYC I was at a session and I cannot remember who, but a woman from Google and I were talking and she stated that they did a test years ago and that when they removed the "I'm Feeling Lucky" button there were a ton of complaints. Most people inquired about something that changed on the site- but could not point out what it was....
Forum discussion continues at Sphinn.