http://www.youtube.com/watch?v=K-_T949uSwU
http://www.neowin.net/news/microsoft-street-slide-street-view-will-never-be-the-same

I've seen that on Google Maps Mania, it looks really great.
http://googlemapsmania.blogspot.com/2010/07/microsoft-street-slide.html
And some people trye to do the same with Google Maps API now ;)
http://homepage.ntlworld.com/keir.clarke/web/street3.htm

I've just added a fourth version of that demo.

http://homepage.ntlworld.com/keir.clarke/web/street4.htm

Still not as impressive as Street Slide but slowly getting closer ;)