Personally, I think April fools jokes are sort of tired and immature. But if you are going to do one, there is a right way and a wrong way. Don't leave your reader feeling like a sucker.

Here is one that I think was done right:

http://kendalvandyke.blogspot.com/2009/04/undocumented-trace-flag-improves.html

TJayBelt's left enough people feeling like suckers that I think you could say it was not done right. It was way too straight and then at the end it was not funny or clever, so I just felt played.