Author's Note: Based on "looking out the window" by paris20vt. Please view the original photo at http://www.flickr.com/photos/21334906@N08/5657584157/ ...and note that the irregularities at the edges of the window panes are from paint and are in the original, not the result of sloppy selections on my part!
This photo was more challenging to selectively desaturate than I thought it would be! I tried different selection methods for each of the window panes, wanting to get a feel for how Phoenix's handling compared to GIMP (and my fading memories of Photoshop). As it turned out, the "easy" method -- using the magic wand -- wound up needing so much touch-up that it took longer to correct than the others put together. And it didn't come out as well, either, I think. Winner: generous Polygonal selection tool, with eraser for touch-up.
(The tl;dr is almost over.) :p
I wound up only halfway desaturating the land visible between the building and the coast; I tried it both fully saturated and completely desaturated, and neither looked right. Desaturating the more-distant area of coastline darkened it and increased its ontrast too much, so I gave it a slight blue tint matching the sky. I also discovered that an optical illusion, caused by the human eye perceiving pure grays as bluish, reduced the apparent contrast between the grey areas and the blue sky, even after I brightened the sky. So I added a very, very faint reddish tone to the gray areas.
This was really fun! Good luck to all. :D