The image-stitching technology which produces wonderful 3D imagery is available on Live Maps in the form of pushpins; click on one and you'll get a fully 3D experience of the location in question.
Some examples can be seen in Seattle, Cairo, Vatican city, or at the Leaning tower of Pisa.
This is what Photosynth was born to do; being able to explore distant locations in a cool 3D environment is fantastic, and while it not may be a killer feature that'll make people swarm from Google Maps to Live Maps, it's definitely a nice advantage for Microsoft's product. Unfortunately, Photosynth imagery isn't directly embedded in the map; instead, you need to have Photosynth installed, and it opens in a separate window, which partly ruins the overall experience.