Heheh... Yeah, playing with "#!/usr/bin/perl" vs. "#!/usr/local/bin/perl" is something we've done in the past as well -- but that was a case of maintaining both a really ancient "system default" installation for solaris (that was /usr/local/bin/perl -> perl4) along side a not-too-ancient perl5 (/usr/bin/perl -> perl5.3).
It makes life tolerable, but there are still traps for the unwary -- e.g. when scripts are copied in from other places that don't happen to share this subtle distinction in perl paths. Just another of those gritty details that users of perl scripts need to stumble over now and then...
We could also opt for "#!/usr/bin/env perl" as the shebag line, and control the relative ordering of /usr/local/bin and /usr/bin in PATH. But that's not exactly a comfortable solution either; it just passes the discomfort to the user's shell environment instead of the script maintainer's choice for the shebang line, which is probably a really bad idea.