I just had a nasty run-in with PAR. Activestate Perl doesn't play as nicely with CPAN as I'd like, so I usually use its own built-in "Perl Package Manager". The problem with that is that installed packages aren't rebuilt (from what I can tell), they're just downloaded in binary form and unpacked. So you often don't get the latest version that's on CPAN.
PAR was choking on Scalar::Util, because it couldn't find a method named "refaddr". But the program worked fine when run as a .pl; it only choked after being pp'ed into a .exe via PAR. I only need to make a TINY change to this script and re-compile it into a .EXE, so I wasn't really looking forward to rewriting this Perl application just so PAR could read it correctly.
Thankfully I found an answer on Google groups. I coulnd't tell you how many times Google groups has saved me a heck of a lot of time and/or effort. In this case it probably saved me a day worth of work. Even on such an obscure question as this.
Now that I think of it, some advice: Don't use PAR for applications that are going to be used by anyone, or relied upon by anyone. It's not a lot of fun.
Actually, some better advice: Don't use Windows for applications that are going to be used by anyone, or relied upon by anyone. That's better.