a partial Date::Calc solution (see the pod about normalization):

use Date::Calc qw /Localtime Delta_YMDHMS/;
my @then = (Localtime(1112241312))[0..5];
my @now = (Localtime(time))[0..5];
print join ":", Delta_YMDHMS( @now, @then );   # S,M,H,D,M,Y
[download]

To get the number of weeks difference, either do:

use Date::Calc qw/Delta_Days/;
print Delta_Days( @now[0..2], @then[0..2] ) / 7;
[download]

Or use the Weeks_in_Year and Week_of_Year methods.