Me too. Checked it out. Gives long string of diagnostic info, with "Vehicle Speed" one of the items, digitally displayed to 0.1 mph. Wish it were one of the regular display options, since the analog speedometer is hard to read accurately.
Too much bother to do on regular basis, but maybe worth it for a long highway trip where you want to set cruise spot on? Maybe not.
2011 GT Coupe - candy red, auto, all the options
Mods - Roush supercharger, FRPP Sport axle-back mufflers, Forgestar CF5 gloss black staggered wheels