Here's another option:

use Modern::Perl;

my %hash;
map { /(.+)?,(.+)/; $hash{$1}{$2}++ } <DATA>;

say 'OS,RELEASE,Yes,No';
say "$_," . ( $hash{$_}{Yes} || 0 ) . ',' . ( $hash{$_}{No} || 0 )
  for sort keys %hash;

__DATA__
Ubuntu,Warty,No
Ubuntu,Hoary,No
Ubuntu,Breezy,Yes
Ubuntu,Breezy,Yes
Fedora,Yarrow,Yes
Fedora,Stentz,No
Fedora,Yarrow,Yes
Fedora,Yarrow,Yes
Windows,XP PRO,Yes
Windows,XP PRO,Yes
Windows,XP Home,No
Windows,XP PRO,Yes
[download]

Output:

OS,RELEASE,Yes,No
Fedora,Stentz,0,1
Fedora,Yarrow,3,0
Ubuntu,Breezy,2,0
Ubuntu,Hoary,0,1
Ubuntu,Warty,0,1
Windows,XP Home,0,1
Windows,XP PRO,3,0
[download]