People wanting to buy maps for their websites (or for offline purposes).
People wanting to find local services (there are pubs, garages etc shown where I stay). Local Services could pay to get listed. Local search seems to be one of the aims of Google just now - bringing the smaller local companies/services who perhaps don't use the web or don't appeal to a country wide market into the picture. People often want to know about local services in their area. If Google offers it then people (worldwide) will use Google.
Auto route systems for car journeys. In the future you may be able to pick a starting and ending desintation with google showing available flights (with links to the airline = affiliate revenue) and hotels in the area.
If detecting that you're travelling to a tourist attraction it could offer to sell you tickets.
Google probably doesn't fully know where this technology could go / could be used.
If I was a shareholder of Google I would be quite happy. Google knows that other companies will show inovation and move in on Googles market. Instead of sitting back and waiting for competitors to emerge (having to react to things) Google has became is own worst competitor! By that I mean that someone at Google says "If I was Google's compeititor what technology could I develop to threaten Google / take its thunder". Then it goes and builds that technology for itself.
It's possible that it was released to be a distraction to their competitors. I'm about to ban it from the office. It's by far the biggest time waster we've had in the office in a LONG time. Trojan Horse, right?
I can't figure out the practical use. Maybe in an offline-only version they could take the desktop Mappoint software on (which I find extremely useful and keep with me everywhere), but I can't imagine that revenue source is that great for Microsoft.
That said, they do have some interesting case studies on their site for practical applications of Earth in commercial enviornments. Time will tell.
Jake, I'm sorta glad I don't work in your office :-)
In my office I am busy marking local real estate listings and attaching associated links and general information. I plan to add the marked map to my websites/blogs! This is the "coolest" tool I have ever seen!