I've had pretty good luck everywhere I had cable internet, not much in the way of regular outages. Obviously a limited sample, I haven't lived too many places, but at least living where toast0 has lived is a scenario where cable internet is reliable. Not my current address though, cause Comcast won't service it.

Certainly, there's problems in some part of the network, and getting past level 1 tech support is hard. Physical security is pretty much unlikely. That said, I don't think those boxes are going to take much abuse to open even if they are locked.