Hi timfitz, welcome to GE!

Depending on WHICH placemarks you're looking at, they can either reside on your own PC or are actually part of the Keyhole Community BBS layer, streamed to you from the Google Earth servers.

Basically, if a placemark is posted on the BBS, then it will probably end up in the BBS layer at the next database update.

Keeping your placemarks neat and organized (and archived out of GE on occasion) is an outstanding habit to get into.

I've been using GE more as a teaching tool (for both myself and my children) than as a "golly! wow! look at the Statue of Liberty!" sort of thing. Creating tours that explicitly map out the history or significance of an item or place is very rewarding, both to myself and to my "pupils". As several here on the board can tell you, I'm fond of adages. A favorite is "Those who forget the past are doomed to repeat it". It's something I'm trying desperately to instill into my children - GE is shaping up to be the tool that I need to accomplish that task!

Again, welcome to Google Earth, and the Keyhole BBS.