I was cruising a major highway in MA and the mile markers were in tenths of a mile. 70 on my speedometer is actually 60. Now I realize why I always have people on my tail and get such great mileage; I'm going 10 MPH slower than I think I am! No tix in ten+ years though.
Varooom
Usually, that's only a problem if you use tires other than the oem size... or change gearing ratios.
There are boxes you can add to correct the speedo...
Have a look in the accessories area - there are speedo healers etc.
http://www.vulcandrifterriders.com/reviewpost/showcat.php?cat=all&stype=1&si=speedometer