I installed Google Earth 4 this morning. I nearly cried :V
Textured buildings are awesome. I recommend heading to Vegas, New York... some of Toronto's done quite nicely, too. Apparently Rome is pretty good, but I missed that one.
London was the best for me - positioning the "eye" next to London Bridge station, looking out over the bridge and being able to see the gherkin... brings back memories of a long bus journey home. Which I could probably route plot, and then flyover.
There were a couple of real landmarks that don't seem to be done yet - Lady Liberty was conspicuously absent, considering that the flagpole on Liberty Island has been done. Also, the CN Tower was one I hoped to see, but is left out. They are both clearly visible on the satellite picture, but 3d models would be nice.