I started riding in north Florida where the trails are tight and snakes are common. If you have a chance to avoid one, obviously that's the best tactic, but when I rounded a corner and there's a snake in the trail and I'm trucking along at 15 mph or whatever, I lift the front and put it down on its head. Rolling over it means it doesn't have a path to strike at you. I don't care for bashing on the heads of little critters, but this isn't a fight I plan to lose again; I managed to get bit while scouting a trail, completely ignoring my surroundings, and snake bites are not any fun. They're pretty durable, too. I've seen them run over by motorcycles and scurry away unhappily.
The worst part about seeing a snake on trail for me is that every root in the trail becomes a snake for the next hour.