Juerd solution is a good one
But if you want an easier to understand
solution you could use good old fashion
flag variables

#!/usr/bin/perl -w
use strict;

my (@desc, @data);
my $pushOnToDescFlag = 0;
my $pushOnToDataFlag = 0;

while (<DATA>){
    if (/^Description:$/){ 
        $pushOnToDescFlag = 1; 
        next;
    }
    if (/^Data:$/){
        $pushOnToDescFlag = 0;
        $pushOnToDataFlag = 1;
        next;
        }
    if ( $pushOnToDescFlag == 1 ) { push( @desc,$_); }
    if ( $pushOnToDataFlag == 1 ) { push( @data,$_); }
}

foreach my $d (@desc) { print "Desc = $d"; }
foreach my $d (@data) { print "Data = $d"; }

__DATA__
Description:
yada_d1
yada_d1
yada_d1
yada_d1
Data:
yada_d2
yada_d2
yada_d2
yada_d2
[download]

... I believe to be a matter of style
and what is more important to you
Streamline code vs. readability
IMHO