user guide (PDF version) for version 4 beta of the useful and fun Google Earth (most people know about Google Earth's virtual globe with maps/satellite pics of the world etc you can zoom around live, but if not see Google's "five things" - Google Earth is downloadable here). There's also a user manual for version 3.
One gotcha to note - when I first installed Google Earth I scratched my head for ages trying to find the "Keyhole Community BBS layer". There were loads of exhortations in the Places panel to "Enable the Keyhole Community BBS layer in the Layers Panel at the lower left." But where on earth (if you'll forgive the pun) is the Keyhole Community BBS layer, you may ask? There's no listing in the Layers Panel that actually reads "Keyhole Community BBS".
Well it's actually labelled "Google Earth Community" - that's the one you should tick in the Layers Panel. It's the same thing. Yeah OK, I should have clicked the Keyhole Community BBS link immediately and then I'd have worked it out. But people shouldn't have to take time figuring this sort of thing out, it should be called the same name in both panels. (Muttering about usability and lack of clear simple instructions again - my usual bugbears...).
There's more helpful stuff and active help on Google Earth at the Keyhole BBS/Google Earth Community forums.