I've also seen some reviews saying the valve was a problem, but I've never had a problem with it. You're not supposed to monkey with it once its turned on anyway. The electric pressure cookers have a pressure switch, thermostat, and physical valve, so they're supposed to be unable to explode. My cooker's similar to Jim's in the first couple of posts, it looks like the same guts, but the brand I have has an inner pot that comes out, has a non-stick coating not stainless steel. There's the stove top model reviewed at that link, the Fagor brand, here's a YouTube of one that exploded. I think they had the flame too high, overheated.
I found this story with video about a lawsuit for the Power XL. From the story, it seems they took the lid off while it was still under pressure (although it's not supposed to do that). Then there's the problem of superheating, where if you expose something really hot to the cooler ambient air, even if you shake something under pressure, it can explode; this is also a major problem in foundry work. No pressure cooker can be taken lightly, it should not be moved and certainly not shaken when under pressure.
http://miami.cbslocal.com/2015/06/24...e-cooker-case/