There has (IMHO) been some misconceptions about exactly what this is, the hype (and I partly fell into the same trap) seems to surround its bringing Google Earth (aka 3D) to the browser – which it certainly does, but as Ed Parsons notes:
“in that context it should become clear that the big announcement of the Google Earth plug-in, is more about adding a API to earth, than bringing 3D functionality to the browser.”
its not the biggest thing – its that it opens Google Earth to scripting!

And being browser based brings reasonably familiar, and cross platform, Javascript to the table, effectively obsoleting the unsupported COM API (and ActionScript?).

As many blogs note 3D in the browser is not that new, LiveMaps (or what ever it called now. virtual earth?) has had it for a while, not to mention WorldWind (java), and the myriad of other 3D globes.

(however the one area this is good on the web, is it allows much larger datasets to be displayed and intereacted with – in already existing Google Maps API mashups – with little work)