Considering Flickr's 20,000+ photo uploads per minute and 2.5 million photos being geotagged this month (only 5 days into the month), I could definitely see a benefit of someone creating a Photosynth/Flickr search and select interface with a Flickr API that would allow Photosynth users to select public download permissioned photos to use in creating Photosynths. Seems there are hundreds of online resources that have been already created using Flickr API, this would just be the most mind blowing one begging to happen. I'll just about bet you MS folks already have one, just not yet released (wink). I would guess any licensing issues would already be addressed in the same fashion the other API resources have.
FYI - A Flickr search for "space needle" resulted in over 50,000 photos which can be sorted by most interesting, and most recent. A search for space and needle resulted in over 90,000.