The CPAN module Date::Manip parses most of these dates, but there are some (namely those of format mm-dd-yyyy and 2014-05-30 PST (0)) which it can't parse.

Here's an example, of course you can use any other output format than the "%c" I'm using here.

use warnings;
use Date::Manip;
while (<DATA>) {
        if (/(.*: )(.+)/ and defined($d = UnixDate($2, "%c"))) {
                print $1, $d, "\n";
        } else {
                print $_;
        }
}

__DATA__
xmas.com : 08-Nov-2007
----------------------------------------------------------------------
+---------
jacket.com : 30-Jul-2006.
----------------------------------------------------------------------
+---------
shows.com : 2006-12-20
----------------------------------------------------------------------
+---------
item.com : 22-Aug-2009.
----------------------------------------------------------------------
+---------
...
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