That's needlessly complicated, simply replace the stuff you don't want with nothing (as Anonymous Monk already said): s/\(.*\)//.

The balancing caveat still applies, of course.

Update: thospel is completely correct, my solution above (and Zaxo's) doesn't work for multiple parenthesis in the same string. To fix this (and actually make it recognise balanced parens):

$_ = "111(22(33)44)55";
1 while s/ \( [^()]* \) //gx;
if (/[()]/) {
  print "unbalanced!!";
} else {
  print;
}
[download]