They have them, but bring your own if you actually want to dry your hair. The ones in the room dont do much, its good to be safe and just bring one.
Norwegian Leeward 1996
Royal Caribbean Sovereign of the Seas 1997
Costa Atlantica 2003
Carnival Destiny 2004
Royal Caribbean Adventure of the Seas 2005
Royal Caribbean Empress of the Seas 2006
Crown Princess 2007
Carnival Valor 2009
A hair dryer is provided in the bathroom (Destiny, Triumph, Victory) or at the desk/vanity in the stateroom (Spirit, Pride, Legend, Conquest, Glory, Miracle, Valor). Hair dryers are not provided in the staterooms of all other ships.
I guess they dont have in Fantasy Class and Hoilday class ships so bring your own.