Before I go too far into this, I do recommend that people read the article I linked to and then do their own experiments. The short version is that light that comes from the a cone faster than f/2 (more or less) cannot get to the 7D / 60D / T3i / T4i detector. The camera knows that a fast lens is present and increases the ISO (without telling you) so that you experience a shorter exposure but the same number of photons have arrived at the sensor.
You can test this by shooting a manually exposed image at (say) f/1.4 and then unlock and rotate the lens so that the contacts don't mate. You should see the recorded brightness fall. I've done this and observed it with my 5D2 and so have several others.
Taylor and Talley - I really fail to see how the a wider f-stop can improve the bokeh if the light that supposedly produces the image does not reach the sensor.
Of course, the light transmission from the outer light cone does not drop to zero instantly, so there will be subtle changes from say f/1.4 to f/1.6, more pronounced changes between f/1.6 and f/1.8 and from about f/2 the bokeh will behave as you might expect for the lens.
