...Denethor looks into the Palantir (of Minas Tirith) watching Frodo getting caught by Gorbag/Shagrat in the Tower... so, Denethor loses any hope and fall into madness... stopped by Gandalf who is taking control over Minas Tirith... look here: •
Seeing Stone of Minas Anor...The Witch-King looks into the Palantir of Minas Ithil (now Minas Morgul) and show what he see to Sauron... They are facing Aragorn who is looking into the Palantir of Minas Tirith showing Sauron the only thing he fears: Anduril! Sauron thinks Aragorn got The One Ring now to use it against Sauron... look here:
Ithil Stoneboth Scenes were cut out of the film... even in the extended version... :-( I would like to see those scenes too!
...as Pippin looks into the Palantir in Edoras... Sauron thinks that Saruman got the Hobbit with the Ring... because it was
the Palantir of Orthanc... and Sauron didn't know, that the Palantir wasn't there anymore...
so what do we learn? If wee take a look into the Palantir, we see things... real things... BUT: in all cases shown above, all characters thaught false... even if we see things that are right our conclusion may get false... so, I am not wondering why there are some peoples (here on the board) getting sickofpalantirs (sorry for that joke ;-))