As some of you may know, there are several engineering effects which allow you or others to temporarily become a chicken. One is the Poultryizer (used on others). It's also a random effect that may be applied to you via transporter malfunctions.
Blizzard has done a lot to prevent unintentional mounting, particularly in the recent patches. Mounting as an Ogre is no longer possible on live.
However, you CAN still mount while polymorphed into a chicken.
You need an Orb of Deception or a Halloween Candy. After being polymorphed, use the disguise effect.
While the disguise effect is active, mount up.
After mounting, cancel the disguise buff and what you're left with is a mounted chicken.
http://img142.imageshack.us/my.php?i...8145929nf2.jpg
As for how this is useful?
Well, it can be useful in PvP in very limited situations. If you get polymorphed and remain polymorphed after the mage/engineer is dead and you are out of combat (but still polymorphed), pop the disguise effect, mount up and ride away. (Or take a taxi.)
This could save you from another fight assuming a mage or engineer gets off a polymorph right as they die and their buddies are charging you.
For me, I use it to hop on the taxi path faster after a transporter malfunction turns me into a chicken, rather that waiting three minutes for the debuff to wear off.