Re: My favorite silent English letter is:

[tobyink]

Does v in "revving" really count? In my books it's the same as the double l in "falling" - the two letters in the double are not pronounced separately from each other, but they act to disambiguate the pronunciation of the preceding vowel.

I'd expect "reving" to rhyme with "leaving".

Bringing things back to Perl, the parentheses are "silent" (useless) here:

my $foo = (__PACKAGE__);

But act as a disambiguator here:

$foo{(__PACKAGE__)} = 1;