Cemetery question for our Jewish friends?

http://www.kolel.org/pages/reb_on_the_web/stoneson...

It's a form of memorial (which is what Buddhists construct pagodas for too).

We are taught that it is an act of ultimate kindness and respect to bury someone and place a marker at the site. After a person is buried, of course, we can no longer participate in burying them. However, even if a tombstone has been erected, we can participate in the mitzvah of making a marker at a grave, by adding to the stone. Therefore, customarily, we place stones on top of a gravestone whenever we visit to indicate our participation in the mitzvah of erecting a tombstone, even if only in a more symbolic way.

Yes.

It is a symbolic act. It is a very important kindness to bury the dead. By leaving a stone you are symbolically continuing the burial and honoring the departed by this little addition.