I really didn't want to hear that. I haven't experienced any problems with this (yet), but what might I expect to happen? Or am I safe because it's within a BEGIN {} block? I could see it causing problems in the middle of the script, but if it's a one-time switch before anything else happens?

C:\>Apache -V
Server version: Apache/2.0.48
[snip]
Architecture:   32-bit
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/winnt"
[snip]

C:\>perl -V
Summary of my perl5 (revision 5 version 8 subversion 2) configuration:
  Platform:
    osname=MSWin32, osvers=4.0, archname=MSWin32-x86-multi-thread
[snip]
    usethreads=undef use5005threads=undef useithreads=define usemultip
+licity=def
ine
[snip]
  Compile-time options: MULTIPLICITY USE_ITHREADS USE_LARGE_FILES PERL
+_IMPLICIT_
CONTEXT PERL_IMPLICIT_SYS
[snip]

C:\> more c:\apache2\conf\httpd.conf
[snip]
# WinNT MPM
# ThreadsPerChild: constant number of worker threads in the server pro
+cess
# MaxRequestsPerChild: maximum  number of requests a server process se
+rves
<IfModule mpm_winnt.c>
ThreadsPerChild 100
MaxRequestsPerChild  0
</IfModule>
[snip]
LoadFile "C:/Perl/bin/perl58.dll"
LoadModule perl_module modules/mod_perl.so
[snip]

C:\> more c:\apache2\www\port80\test.pl
#!c:/perl/bin/perl -w
$|++;

BEGIN { chdir "C:/Apache2/www/port80" }

use strict;
use CGI::Simple;
[snip]
[download]

Basically, the issue is that chdir changes the current working directory, but that is global to the process, not to a thread. The result is that if anything else does a chdir, you will no longer be in the directory you thought you were in.

For the most part, as long as all of your scripts chdir to the same place you should be okay. You can probably assume that Apache 2 and mod_perl 2 will not do any chdir stuff, but other CPAN modules might. Best to test with high currency and see what happens, as well as grep'ing any modules you use for chdir.