jynx, your sub does not even return the correct answer the first time, if $b has been set elsewhere -- you rely on it to be numerically zero initially. Moreover, you will get a 7, not a 0, for Sundays ... so on the whole, I can't say I like it.

That is not to say my answer cannot be trimmed down. Indeed, I just did. And just so as not to leave your suggestion as the best (sorry; I really don't like it), I trimmed it to 46 chars:

sub f {
#        1         2         3         4         5
#234567890#234567890#234567890#234567890#234567890#23
$b+=!($_%4||/00$/&&$_%400)for 0..($b=pop);$b%7
}
[download]

Comparing that to my first suggestion ... can you tell I really like the ternary operator? ;-)

The Sidhekin
print "Just another Perl ${\(trickster and hacker)},"