I rode a pacer once, a standardbred off the track that the seller said used to belong to Michael Landon. Not sure if that was true, but the pace was really weird to ride. sitting, you felt you were moving side to side more than forward.
It's horrible.
And impossible to break them of it.
Racing pacers can sure fly though. Some people have started crossing Standardbreds with Racking Horses to get Speed Racking horses. There's a high dollar class in the Racking Horse Celebration for Speed Racking and it's awsome to watch. But truth be told, a lot of them are pacing instead of racking. Not good in my book!