While boarding my plane this morning, a Virgin Atlantic flight bound for London Heathrow scheduled for a 0820 departure, right before I got on the plane there was a policeman with a sniffer dog. I've been going to Newark or JFK for about 3 or 4 times a year since the October after 9/11 and this is the first time I've seen sniffer dogs. Apart from the turbulance which was the first thing that's made me scared in a long time, the flight was fine and actually quite empty.

Has anyone else seen this, or know why it's going on now?

While I've never been to that airport, I think its safe to assume that in probably 90% or more of cases sniffer dogs are called out to deal with possible drug smugglers, or other contraband not aloud to be taken past customs. So unless that is your thing, I dont really think there would be too much to worry about

Dogs are on duty almost all the time in airports. We just don't get to see them. Most are working in the baggage areas. The basic reason to take the dogs out in public, is for public relations. And I imagine occasionally, to cause a person to give themselves away when they see them.