Cool site overlays semi-transparent USGS-like [actually Ordnance Survey -Ed.] map over aerial photography. Move your cursor over the map to see moving image swap. GlobeXplorer had it here in the US last year.
http://www.multimap.com/map/photo.cgi?client=public&scale=1000000&ukwidth=113&ukheight=113&lang=&uk.x=65&uk.y=65

Manifold Conference; georeference.org are organizing the first ever Manifold User Conference for November 18 and 19 at Cornell in Ithaca, New York. The two-day event features a look at what users are doing, the future of the software and many opportunities for user input. And, it's affordable. Details on online here with registration here.