I'm with blazer on this one, I don't like all those variables names. Having to take "username" by slicing the 5th element from your array is creating depencies on the order of your data. I'd have read the data into hashes in like this.

use Data::Dumper;

my %on_prop;
my %on_user;
while (<DATA>) {
    my @fields = split "\t";
    my %column_data = map {$_, shift(@fields)} qw(PROP COLOUR TXTCOL U
+RL360 USER YOUR_NAME ETC);
    $on_prop{$column_data{PROP}} = \%column_data;
    push @{$on_user{$column_data{USER}}}, \%column_data;
}

print Dumper(\%on_prop);
print Dumper(\%on_user);
print  scalar @{$on_user{'rob'}}; # prints 2 (more than one item for t
+his user)

__DATA__
123    Red    blue    whatever    rob    blah    blah    blah
124    Red    blue    whatever    rob    blah    blah    blah
125    Red    blue    whatever    jon    blah    blah    blah
[download]