Compact jQuery tool tip code, without jQueryUI
Bind method should be used only when if your element is not loaded into DOM on pageload. So you could attach events to it using bind after wards. also if your using jquery >= 1.7 use 'On' method to achive it. but as per your js fiddle you don't need it at all.

second you could declare a variable to store the jquery object of follow. Make sure about the variable scope though.

var follow=$('#follow');

$('div.a').mousemove(function(e){
    follow.css({
       left:  e.pageX + 20,
       top:   e.pageY
    });
})
.mouseenter(function() {
    follow.css('display','block');
})
.mouseleave(function() {
    follow.css('display','none');
})