It depends on the situation. Those dogs that just stand and bark as I go by, I ignore. If they seem inclined to chase me, and I'm moving at a pretty good clip, or I have a downhill run coming up, I just sail away from them. But if they're heading toward me and I don't think I can outrun them, I get off the bike and walk, keeping the bike between them and me. I've heard that a rider's height and speed is seen as a challenge to some dogs who are guarding their territory, and the rider appears less threatening when he's off the bike and walking. Whatever the explanation, it's never failed to work for me yet. I just used this trick yesterday morning on two large dogs who were barking and advancing across the street toward me as I started up a hill. When I got off and started walking, they stopped following and just barked as I walked away. When I got to the top of the hill I got back on and rode away, and they didn't pay any further attention.

Of course, dogs can be unpredictable. On my 17th birthday, as I rode out of my driveway, a neighbor's dog that had ignored me for three years ran across the street and bit me on the leg. I didn't even try to avoid him because I never expected him to do that. (He must have been in a bad mood that day, because when the Animal Control people came to pick him up that afternoon, he chased them away. But after that he went back to normal and never bothered me, or anyone else as far as I know, again.)