1 Gigapixel in Frankfurt
This is 176 images stitched with hugin and enblend, shot with a Nikon D200 + 70-200mm @200mm for most of the bottom part and 70mm for the sky with a Nodal Nijna 5L, from the observation deck in the Maintower. It was very very windy, and the whole tripod+lens shook.
Processed with the OpenGL preview version of hugin, quite awesome! Gimp was not used; exposure was lightened from the underexposed source images with ImageMagick which had no real problem with the size.
Final panorama is 48,161 x 22,562 or over 1.0 gigapixel. The final TIFF image was 2.2GB, compressed to a JPEG 252MB. The image uploaded to Flickr is reduced by a factor of 5, i.e. it contains only 40 megapixels.