If earth can be seen as a infinite pool of electrons, and the
clouds are positive in charge, it would make sense for the current
to flow through the shortest route.
So if the tree sticks out, obviously the current will choose to
flow through the tree and you'll get a shock if you stand next to
it.
Yup
For lightning rod/conductor, it is grounded/earthed. So when
there's lightning, it will induce opposite charges on the rod
(charging by induction), which will attract the moving charges in
the lightning.
There might be more info here... no time to look through yet...
:http://en.wikipedia.org/wiki/Lightning_rod