I like this photo a lot (the composition, the distinctive elements in it, the colors) -- the only thing I might suggest is to try to kick up the contrast or decrease the brightness a little (or both)...it might look even cooler. :) (Of course, this is all according just to my own personal taste.)
How many people who don't know what a handsome cab is have commented on this man's looks? My guess is a lot. Your desaturation level is ok, but not sure it's the best treatment. Try a good b/w conversion with true blacks. Might make this be a better character study.
Very nicely framed and processed. It gives the whole feel of horse and driver in the city, and the parallel blinkers and shades nicely connect man and steed.