It works if I give the full path to Perl, but not if I just type "perl".

Update: I get -(pause) ju(pause)st an(pause)other perl hacker(pause). Timings (733 MHz G4; /usr/bin/perl is 19280 bytes):

real    0m2.349s
user    0m1.865s
sys     0m0.207s
[download]

It seems that on my system the bulk of /usr/bin/perl has been separated out into /System/Library/Perl/5.8.6/darwin-thread-multi-2level/CORE/libperl.dylib (1086420 bytes).

perldoc perlvar says:

Depending on the host operating system, the value of $^X may be a relative or absolute pathname of the perl program file, or may be the string used to invoke perl but not the pathname of the perl program file.

and

It is not safe to use the value of $^X as a path name of a file, as some operating systems that have a mandatory suffix on executable files do not require use of the suffix when invoking a command.