Windows Live Maps has updated some of its imagery, adding Miami to the list of cities you can explore in 3D, as well as updating to high-res imagery for numerous other locations.
To show the difference between high-res and the standard imaging, I zoomed in to maximum detail for Portland and Manhatten, using cars as the reference points. If you can ignore the obvious "stitching" between the old and new imagery, you can see how improved the sharpness and clarity of the high-res images are.
The update seems to be as follows:
3d: Miami
High-res: Manhatten, Portland, Bellevue, Miami, Philadelphia, several areas of California including San Diego, and for those north of the border; Hamilton, Ontario.