Try this:

#! /usr/bin/perl -w

use strict;
use Date::Manip qw(ParseDate);

print ParseDate("1 day ago") . $/;
print ParseDate("7 days ago") . $/;
print ParseDate("14 days ago") . $/;
[download]

Date::Manip is fun to mess around with, I'm surprised at the kinds of "fuzzy" descriptions it can handle.

update: I didn't search carefully enough to see that cazz had already mentioned this module.

update: In the interest of good form, added the import list. Is it kinda uncool that ParseDate is exported by default?