Got to say, having lived in the country for pretty much all my life I always slow down for horses on the road, its common courtesy. I have still had the odd rider giving me the "Wave" for "speeding" past them even though I had slowed down for them.

IMO, there are as many "chavs" on horses as there are driving scoobs now... the bad ones always show the rest of us up... and no, I don't have a horse, nor want one (although the wife does... no idea what it is with women and horses).