A few of the best April Fool’s Day jokes

Google made a search engine results page that no designer could love. Searching for helvetica on google.com gave a search engine results page rendered in Comic Sans.
Google's helvetica april fool
Foursquare had a more subtle approach on its check-in page, where the user was told that they had secured no points.
Foursquare's April fool
LinkedIn took a literary and scientific turn with a Wold Newton-esque twist on its ‘people you may know section’
linkedin April's Fool