Microsoft announced today the integration of Photosynth with Virtual Earth, enabling free navigation of photos in 3D on the web. The NASA offers an example of the results (Silverlight required). Photosynth has been publicly available since last summer. It somehow competes with Google's Panoramio and even Google StreetView since Photosynth have exploration in Virtual Earth capabilities (even on the iPhone!). You can also make private 'synths' with MicroSoft's GeoSynth. Hotels and travel sites are amongst those expected to use this free 3D photo browsing on the web opportunity from Microsoft. With the release last month of the Google Earth 5.0 Plugin for browsers, the battle is heating up.