[Kalimac]

The Palantir's function seems to be a little fuzzily defined; like Birdland already said, when Pippin first encounters it, it's like he's picking up the phone so that (Sauron thinks) Saruman can prove that he's there. (On the "Say sump'n to da Boss" principle). OTOH when Denethor uses it its function seems a little more general; he's described as seeing what's happening in many different places - Sauron, via his own Palantir, is of course selecting and editing these scenes so that Denethor will only see the things that will discourage him, but he does see the black fleet sailing down the river and similar things, so presumably the Palantiri can also pick up a fairly wide range of signals, but on a party-line basis - Sauron can show Denethor what he's seeing in his Palantir, and vice versa.

From all this it seems like a lot depends on the strength of the person using the Palantir; the more powerful they are, the wider range they have - and the more ability to prevent other Palantir-seers from seeing inconvenient things. In the case of Pippin (and, eventually, Denethor) they are both much weaker than Sauron, so they see only what Sauron shows - this would explain why Pippin saw a few Nazgul flying around in the Palantir before the Eye "came on" so to speak. He was seeing what Sauron was seeing.

So after that huge buildup (sorry [img]smilies/wink.gif[/img]) - no, I really doubt Aragorn would have looked for Frodo and Sam. For one thing it probably would have taken more time than he could spare, for another thing there would be a huge risk of Sauron somehow picking up on it - not necessarily on the fact that Aragorn was looking the Ringbearer specifically, but on the fact that he was looking over a deserted and useless stretch of Mordor with a fair amount of attention. Hmm, what could he be looking for? The last thing Aragorn would want would be to divert the Eye back to its own country at that point.