According to this article, Mt. Ranier is showing signs of doing something. This is a good news/bad news thing; while the thought of possibly two volcanos making the landscape dance in one area delights me, it would truly, truly suck for a lot of people if Ranier cuts loose.
From what I've read, the big threat with it isn't considered to be explosive eruption, it's lahars- mudflows. The top of the mountain has been slowly rotting into clay over the years due to sulphur dioxide leaking to the surface, mixing with water to form sulphuric acid, and soaking into the rock. I don't have the book handy, but the Osceola mudflow /name?/ some hundreds of years ago traveled for many miles from the mountain and left deposits many feet deep; deep enough to fill in rolling hills and make a plain. And since such a flow, and landslides, can travel more than 100 mph... I forget how many towns/cities are in the risk area, but it includes a lot of people. And since there might be little or no warning of the actual event, this could truly be an "Oh S**t " moment as you look out the window.
An amazing thing, but definately one to see from a distance.