Haber de vs tener que
 

Hi,

What is the rule of thumb for using these expressions? It's pretty obvious that haber de is a rare bird; where is it appropriate/indispensable?

I was taught that haber de is less imperative. I hear Spanish a lot, and rarely hear haber de used. By the way, hay que is pretty common, but when used it seems less didactic to me than than tener que.

Hay que is pretty common indeed. It looks like yet another take, though :)

Meanwhile, the only "real life" example of haber de I ever stumbled upon is this:

...
Y antes del amanecer la vida le han de quitar
...

I'm just trying to get the real taste of the words (life must be taken away?).

Maybe not the most common, but I think I hear "Habías de <hacer algo>" with relative frequency.