Launching Gmail on April fools' day was, for me, hilarious. At a time when Yahoo! and Hotmail were offering 5/2 Mb, Google came out with 1Gb. It was so obviously an April Fools' joke... but then... wow!
But I can see that from their perspective it caused a lot of confused users - although it probably kept the story in the news a day longer than it would have been otherwise.