Some notes on groups that do data collection in order to have a better idea of the size/character of their users.
http://www.mozilla.com/en-US/legal/privacy/firefox-en.html (in particular, ‘automated update services’) opt-out; all data is gathered purely from information in http headers in updates, so no extra tech built in.
http://ma.tt/2008/07/26-by-the-numbers/ (look for ‘update system’; can’t find other details)
http://civicrm.org/node/274 (current system)
http://civicrm.org/node/430 (proposed collection for next release)
found it useful; twice as many Joomla-based users as expected
data heavy- more to get a sense of what features people are using, rather than how many users there are. opt-in as a result of privacy concerns; over 30K opt-in users.
Web site for UDC: http://www.eclipse.org/epp/usagedata/index.php
Two communications regarding UDC: