i prefer to play on 3 decks but i find alot of dj's who play on 3 think that they must have 2 records playing the entire time no matter what, or they think they are really special if they have 3 tracks going at the same time or whatnot. there are many ways to go about using the third deck but the whole "look Ma, 3 decks!" attitude is pretty lame.
also if a promoter asks me to play on 3 and then has crappy monitors i will completly ignore the 3rd decks because if you arent able to EQ your shit properly then what is the point of using the 3rd deck because it will sound like ass.