I like it, especially the "virtual" birds eyed view when zoomed out more. Also the fly in transition to streetview is nice.
BUT even just sitting there doing nothing it uses 30% CPU and when it transitions to something its up to 70+% and my fans spin up like crazy.
Silverlight in general is very slow for me, I can't even watch any video in fullscreen because all I get is a slideshow. If only I could get it to work maybe i would even switch to bing maps.