Google Earth Pro has been made free by the fine folks over at Google. Note the word pro in there, as Google Earth itself has been free for basically ever anyway. It is a pretty cool tool to play around with, but outside of the professionals that will be using the pro components it is really that much advantage and can get kind of cumbersome compared to the regular Google Earth.
To get it, all you need to do is go to this link, agree to the TOC, and download the program. When you are installing it, you will need a key to unlock the software and that is GEPFREE. A few minutes later and you will have your feature rich professional version of Google Earth running on your computer.
So what does this get you? It goes a slightly higher resolution, where available, as best as I can tell. That is the one perk that is almost worth while. The other perks that it includes is things like estimated measurements and distances around various objects that you can find on the map. Those are fun things to play around with, but short of actually needing that in a professional way, it is really not that beneficial.
Anyway, for what is play around and have fun with it.