There are two great April Fools Day jokes online today: One played by an English newspaper called The Guardian, and one by Google.
The Guardian announced this morning that they would be switching publications entirely to Twitter, and will be adding the archives as far back as the 1821 shortly thereafter. Read about it here.
Google email introduced CADIE: Cognitive Autoheuristic Distributed-Intelligence Entity. This program apparently can configure replies that best suit the tone, language, punctuation and emoticon use, etc. "It's just like you, but automated."