on crowdsurfing...this is dumb, but would make sense, but wouldn't be allowed, since crowdsurfing usually isn't even supposed to be aloud (at least the gigs i have been to)
 - have a few scales at the entrance.  if you are over 150 pounds, you should have a special wristband, which means you can't crowdsurf.  
i find crowdsurfing pretty fucking annoying too...but nothing is worse than some 240 pound smelly fuck that takes every bit of effort to keep up.
on yelling during acoustic parts
 - i think that this is thanks to "metal heads" who view acoustic parts as filler between the kickass kill everyone parts.  so, i suppose for that type of person, an opeth show is ideal.  the quite parts are time to go get a breather and yell "fuck yah" in anticipation of chaos.  
that is fucking annoying.  during quiet parts, i sometimes have trouble hearing the band at all.