I too am curious on what the advantages are of the "Pro" or pay version of Goggle Earth over the free version. I searched on-line and it appears the free version is mainly for personal use, (go figure), where the paid version is mainly for business use.
Couple of the main differences I "read" about from comparisons, and I think "could" be used by us peasants are: better printing and movie making. The viewing resolution is the same no matter what version is used apparently.
Let me mention something about the movie making part, which my next statements are a guess. I ran into a web site: moto-viking.com. which shows a trail riding video along side is a gps tracking route view. Though the loading takes forever, it looks like these guys have combined video and route tracking viewing right next to each other. The route tracking looks like its from goggle earth "Pro". Hence, I think these guys have a paid version of goggle earth and use the movie making part from it. Major geeking going on here, giggle. If I used something like this, I would wait until winter when I can't ride much. Otherwise...
But to be honest, I've never ran into anyone that uses the paid version, even from a business. I too would be interested in feedback from someone who has used both and can tell us the diffences "in plain English", and if it's worth the cost.