Due to the type of driving I do and the way I drive, I always get a lot of miles out of my brakes. I periodically would look in to check mine and everything always seemed like normal wear with plenty of material left.
However, at nearly 80,000 miles and with us 300 miles away this weekend, all of a sudden I started getting metal on metal coming from the front when I applied the brakes. On top of that, there was a lot of pedal travel, so much so I thought I might lose the brakes altogether. We limped home by using the engine to do most of the braking.
When I pulled things apart, all of the pads except one had a little less than half of the pad left. The exception was one of the inner pads that had no pad material at all. It had obviously completely separated from the backing plate. I don't know if this was just a fluke or if others have had a similar experience but I just wanted to let others know.

That was my initial thought but when I looked at the pins, there wasn't any corrosion and they were still well lubricated so I figured I better look a little further. In looking at the pad, there was absolutely not a trace of friction material left and then I found a decent sized chunk of pad wedged between the caliper and the rotor. Putting 2 and 2 together, it was pretty obvious that the entire friction material had become unbonded to the backing plate.
"did the symptoms come on suddenly or gradually?" For the week or so before, it felt like there was some additional pedal travel that I wasn't used to but the major problem came all of a sudden about a block from my mother-in-law'* house. Since I didn't want to be stuck there any longer than I had to be, that'* why I decided to limp the 300 miles home.