I use a lot of Perl 5.8 at the LoC because it's the only dynamic language that comes installed by default on Solaris 10. That, and because it is the primary language of a proprietary product that we have to use. I'd love to use Perl 5.10, but then I'd have to install it on all of the machines on which my code is expected to run. If I had that kind of control, I'd skip Perl and go straight to Python or Ruby. (Actually, that was a lie, I'd use Common Lisp if I could.) As it is, I've standardized on Perl 5.8.
The product I am talking about is Signiant:http://www.signiant.com/.
It's a file based workflow application that basically that is written in Perl in the same sense that emacs is written in emacs lisp. The idea is for people to write workflows in the embedded Perl environment which is the same across of the machines on which Signiant is installed. I could use another interpretor, but that would require extra work and I wouldn't be able to use a lot of the Signiant specific code.
