I've played with other satellite imaging and mapping software, but this blows them all away. Rather than giving you a detailed explanation about it you can get all of the details and download at the link above, or take a Product Tour.
The Resolution varies around the globe, and unfortunately my home town in Southern Wisconsin (relatively small) has very poor resolution, but most of the larger cities I looked at were fair to very sharp.
Below are 3 downsized images of a Las Vegas intersection facing one of the casinos. The original sizes were much easier to see but of course too large for posting. The last image because it is only 100 feet above ground level starts deteriorating so I hot linked it (clickable) to the original size. Note the casino shadows, and that in the last two you can plainly see the people entering and leaving the casino.

Overhead from 3000ft with great detail, note the casino shadows

Overhead from 300ft and still fair detail

Resolution is deteriorating at 100ft (click for full size)
Actually you can go all the way to the ground, which is what I did at the Indianapolis speedway, unfortunately the resolution was poorer than most. This is where another feature of Google Earth is nice. You can rotate and tilt flat, then do a fly through cities, the countryside, or in my case the speedway race track (below).
Yep, I took a lap around the track controlling the direction with the mouse and the forward motion with the arrow up. Here is a tanker truck of some kind I passed. Apparently it was on the track when the image was taken.

As I approached the truck from the rear

Overhead view of tanker truck
Then I stopped out of curiosity and moved to overhead view to see if I could make out what the truck was. Unfortunately no. Were the resolution as good as Las Vegas and some other cities I would have easily read the logo on top of the truck.











