I live in New Zealand and I use it for checking out rivers and lakes for fishing and access to fishing. Although I have topo maps for most of NZ, as well as topo maps for my handheld GPS, Google Earth is still very useful for getting a better idea of terrain, bush cover etc. I use the measurement tools to work out roughly how far I'm going to need to walk. I also use it to check out tramping tracks and such. Not all of my main area of interest is covered by hi res imagery unfortunately.
When the Tour de France is on I use an overlay with the race route to get a further appreciation of the route and terrain etc.
I'm interested in landscapes so it's good to use to check out various parts of the world.
There's a lot of times when something comes up and someone says "Let's check it out on Google Earth".
I might just add I used NASA WorldWind for some time before GE came out. I changed primarily because there was a Mac version of GE and becase GE had much more high res imagery. Aside from those admittedly important points WorldWind was a better application though, although it's a number of years since used it now. GE has improved over time.