Gonna sound noobish but I feel that this match up is hard to a point it just depends on how aggro you are as a Zss player. Imo you shouldn't approach MK much at all unless you are sure or positive about making the hit if in my opinion never, leave yourself at an out.
I have played some spammy aggressive mk's on wifi the occasional good ones and I usually have trouble with them but from my experience MK really doesn't seem that hard at all the problem with him is that facing him you have to play different and I mean almost totally. To me it boils down to a point of rock, scissors, paper and MK will always have the rock and apparently that beats everything.
Playstyle is one thing it seems butI noticed in all of my matches against him that regardless of my playstyle I usually get beaten down to the rock, scissors, paper attacks wherein I make a choice and if it's wrong I get hit I know most matches can be played like this or this game could just be played Oos but he seems to be the number one character it must be done on.
So my advice like I read Dakpo say before Camp camp camp camp camp camp camp camp. However I will say Camp camp camp camp HIT Run away camp camp camp camp camp.
Don't believe me? I found a very good video of Patg versus Ally at KTAR5 oh and a small reminder hold on to 1 armor piece as long as you can and not for hitting for moving.
Here's the link watch the 1st match :
http://www.youtube.com/watch?v=SyyM0oGcrH4&feature=related
I like stunning him in his dash.