Here's the answer from perlfaq1:
What's the difference between "perl"
and "Perl"?
One bit. Oh, you weren't talking
ASCII? :-) Larry now uses "Perl" to
signify the language proper and "perl"
the implementation of it, i.e. the
current interpreter. Hence Tom's quip
that "Nothing but perl can parse
Perl." You may or may not choose to
follow this usage. For example,
parallelism means "awk and perl" and
"Python and Perl" look OK, while "awk
and Perl" and "Python and perl" do
not. But never write "PERL", because
perl is not an acronym, apocryphal
folklore and post-facto expansions
notwithstanding.
