Here's the snippet I ended up with - it's not much more than verbatim from plaid's answer.

Ovid's answer looked interesting too, but I try not to take things from people on crack.   <big grin>

Update: Thanks as well to other fine Monks who offered answers.
    cheers,
    ybiC

#!/usr/bin/perl -w

# parse a log file and move lines with important text to top
# of file while keeping sequence within each of two sections:
# important and not-so-important 

use strict;

my $infile  = '/dir/file.in';
my $outfile = '/dir/file.out';
my @important;
my @normal;

open IN,  "$infile"            or die "Couldn't open $infile";
open OUT, ">$outfile"          or die "Couldn't open $outfile";

while (<IN>) {
    s/unwanted text//g;                   # strip unwanted text
    s/more unwanted text//g;              # strip unwanted text
    s/^\s+//g;                            # remove empty lines

    (/important text/) ? push @important, $_ : push @normal, $_;
    }

print OUT @important;
print OUT @normal;

close IN                       or die "Couldn't close $infile";
close OUT                      or die "Couldn't close $outfile";

# END
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