I haven't seen this hint anywhere else, but I've found that in Siri, if you say 'Wikipedia' followed by anything like 'Muppets' or 'Zombies,' it will take you right to the Wikipedia entry for that request. Pretty cool.
[crarko adds: It's going to be a while before I get a 4s, due to my contract. For those who have one, is Siri as amazing as it sounds or is it just a 1.0 version in need of improvement?]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20111025191039482