I've heard and found from my BP, they can be head shy.
It's hard to say what they "like" if they tolerate you doing it to them with no signs of stress then it's probably not doing any harm.
As far as touching the head, I read a post on another forum that said something like this...snakes have 3 things that stimulate them to bite food. Heat, movement and smell. Some will only need one or two of these. So by moving your warm finger in front of it's face you might be asking for a bite.
I don't think that snakes crave the attention and personal contact that dogs & cats do but they might appreciate the heat source along with the opportunity to explore a little. Watch for signs of stress when handling any snake, that is key. And have fun