Google Blogoscoped posted "Google April Fool's Jokes Galore" today. The post featured Google's extensive (all in good fun) practical pranks on/for it's users. The list included everything from a gmail "custom time button" so you can set what time your mail says it was sent all the way to google knowing your future.
Other top dogs in the tech world got in on the geeky fun such as YouTube, Anti-Google Search Engine Lovers, Microsoft and Search Engine Land, Google Calendar's Wake up Land, Virtual Turism Blog (post on google maps sensoring competitors like apple), Search Engine Roundtable, Orkut changed their logo to Yogurt for the day,
For more fun news on Google and other April Fool's Hoaxes:
All in Good Fun -- Jokes For You and the Family.