Some simple squishing down to 49 char:

sub f {
#234567890#234567890#234567890#234567890#234567890#
$b=1;$b+=1+!$_%4-!$_%100+!$_%400for(1..pop);$b%=7
}
[download]

UPDATE - I was just compression what the parent post had, making sure my answer gave the same as that one, but not looking at the real answer. As pointed out below, '!' binds higher than '%', and thus the answer this gives is wrong. Adding parens, and the fix that japhy adds brings this to 53:

sub f {
#234567890#234567890#234567890#234567890#234567890#23
$b=1;$b+=1+!($_%4)-!($_%100)+!($_%400)for 1..pop;$b%7
}
[download]

-----------------------------------------------------
Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
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