Mike Albano writes on his dumping ground for wireless route switch stuff:

I set out to experiment with just how much faster roaming occurs on an 802.1X WPA2-Enterprise WLAN, when 802.11r is enabled. Also, what is the time difference between the two method’s of implementation — Over-the-Air Vs. Over-the-DS?
Rather than explain the nuances of 802.11r, 802.11k and Fast BSS Transition, I’ve included ‘Recommended readings’ at the bottom of this post, which explain it way better than I ever could.

A comprehensive look at newer fast roaming specifications and how they impact client behavior. Very good read, as are the links included at the bottom.

Read more at: 802.11r, 802.11k & Fast BSS Transition Experiment