Can you mash up both Earth and Maps? Chicago Real Estate broker Prudential Preferred Properties certainly had a go. Writes Chris Janseen:

Thought you might like to check this out – been following the progression of some of the Google Earth uses out there to use in my own and I noticed that Prudential have merged the Google Earth local search directly into their Google Maps — it is pretty nice, good middle ground between the desktop GE app with the added benefit of being built right into the browser. Thought you may want to check out some progress of them.

You need to register to use it, it won’t work in Safari, you have to zoom in tight and there are no local listings outside Chicago, but this Google Map certainly carries some of the features that until now only Earth had. Look:

I guess this means the challenge of depicting layers on Google Maps has been solved, at least for placemarks. (Prudential also does a straight-up Google Earth implementation, as explained here.)