The widget/thermometer only shows contributions entered via a particular online contribution page. We needed it to show online and offline contributions from a certain date range (e.g. contributions that were made no earlier than November 1, 2008).
We adapted this from http://forum.civicrm.org/index.php/topic,6081.0.htm.
In /sites/all/modules/civicrm/CRM/Widget/Widget.php
Removed this line:
AND contribution_page_id = %1
and added this one:
AND receive_date >= '2008-11-01 00:00:00'"