According to the US Geological Survey (and the Discovery Channel), the Yellowstone Supervolcano has erupted 3 times recently, 2.1 million, 1.3 million and 640,000 years ago.

If you average out the time in between each eruption, you get 1 eruption every 730,000 years or so. Since the last major eruption occurred 640,000 years ago, the average says that it will happen sometime in the next 90,000 years or so. Of course, 3 eruptions may not be enough to see a true correlation, but its the best I could come up with.

Luckily, according to the Discovery Channel, a major eruption of the Yellowstone Supervolcano wouldn't come out of nowhere. There would be lots of earthquakes, bulging land and even small eruptions that will give an indication that the big one is coming. Hopefully, with enough warning, people can be evacuated from the blast area in time and there will be no significant loss of life (except the animals and ecosystem of the Yellowstone area).

For some good video, from the Scientist-in-Charge at Yellowstone, on eruption information, geologic hazards in Yellowstone, tools used to monitor activity within the park, and much more you can visit: http://gallery.usgs.gov/video_tags/Yellowstone

I don't think it will happen within our lifetime.

But when it does, it's going to be insane. It'll take down a lot of our infrastructure.

Either way, humanity will survive, and there's probably no escaping it, so I don't worry about it.

What I've read/heard is that it is overdue and could happen at any time. I have also read that the recent swarm of earthquakes is _not_ supposed to indicate the supervolcanic eruption because they are expecting more signs like the ground moving upward etc.