This article is from the Digital Broadcast Satellites FAQ, by Brian Trosko firstname.lastname@example.org with numerous contributions by others.
Grounding the system is *strongly* recommended. Of course,
there are installation situations where proper grounding
might not be possible (apartments, RVs, etc.), but in
situations where it is possible, it should be done.
Grounding the system necessitates direct grounding to an
8' grounding electrode, preferably the main electrical service
ground for the house. If a second grounding electrode is driven,
and the system is grounded to that, the second electrode must be
bonded in turn to the main electrical service ground.
This is not necessarily to protect against lightning; although
proper grounding can certainly help prevent a strike, it will not
save your equipment in the event of one. Rather, proper grounding
is to allow the static charge that builds up in the dish a safe
route to drain away. If the system is not grounded, this charge
can run to ground through the receiver, which has a detrimental
effect on the electrosensitive components inside. Also, nearby
lightning strikes can actually induce a current in the cable, and
proper grounding allows this induced current to safely run to ground.
Grounding is actually quite a simple procedure, and the risks
which it alleviates mean that it is worth your time to do it