This is a tilt-shift fake.
For those who are interested, here is the depth-map that I created and fed to the lens blur filter and here is a shot of the various layers of the mask before assigning gray-values..
There's also a version in my photostream with the focus set on the École Militaire made from the same depth-mask.
March 2008: A nice fella named Martin has made a comprehensive tutorial on how to achieve this effect
Eiffel Tilt-Shift II, originally uploaded by Hanna María & Arnar