CSS3 transforms and transitions (Webkit)

Add the vendor prefix in the transitions:

p {
  -webkit-transform: translate(-100%, 0);
     -moz-transform: translate(-100%, 0);
      -ms-transform: translate(-100%, 0);
       -o-transform: translate(-100%, 0);
          transform: translate(-100%, 0);
  -webkit-transition: -webkit-transform 1s ease-in; /* Changed here */ 
     -moz-transition: -moz-transform 1s ease-in;
       -o-transition: -o-transform 1s ease-in;
          transition: transform 1s ease-in;
}

a:hover + p {
  -webkit-transform: translate(0, 0);
     -moz-transform: translate(0, 0);
      -ms-transform: translate(0, 0);
       -o-transform: translate(0, 0);
          transform: translate(0, 0);
}

Update (05/06/2014)

To answer some comments, the reason for omitting -ms-transition, is that it has never existed.

Check:

Can I Use? Transitions,

Can I Use? Transforms,

MDN transitions,

MDN transforms