My experience has been that even with my hearing protection ON, I hear muffled sounds.  Then those muffled sounds become 'normal', and when something happens, the sound changes.  All sounds seem to be attenuated more or less evenly (from a use point of view, not technical) so I just hear a softer "racket" if something goes wrong.
I'm also willing to trade off the 90% odds that nothing will happen with the comfort I get from using them...and that if something DOES happen, the 90% odds that I'll catch it.
For that situation that falls through all those odds...  well...   /forums/images/graemlins/tongue.gif  I'm up the creek  /forums/images/graemlins/tongue.gif