OK, I heard lots and lots of stuff about Google Earth so far. Yesterday, I actually installed it on some not-so-free-OS box and gave it a try. Two things are floating on my mind now:
I "browsed" different parts of the world and got more and more fascinated... and scared. For instance you can see the Statue of Liberty, and if you zoom in enough, you see people walking around on liberty island! Nice on the one hand, major security and privacy problem on the other hand.
There are loads of interesting ways to use Google Earth, e.g. over at Google Earth Hacks. I'm afraid most of my spare time during the next few days has just crumbled to dust... Now, if they would only port it to Linux, that'd be really nice...