A lot of effort has been poured into the upgrade routines for Coder Upgrade as evidenced by the green check marks on this page. (A side note: so far, duellj is the only person to show up for the upgrade barn raising and much thanks to Jon is due. If you are up for a challenge, help is still welcomed and needed to write and/or test routines.)
An interesting example of an upgrade routine is the theme() function call change. This upgrade involves "array-itizing" the variable parameters. For example, this:
theme('user_list', $users, $title);
becomes in D7:
theme('user_list', array('users' => $users, 'title' => $title));
The twist involves finding the keys for the associative array of variables.
Sparing the details, Coder Upgrade will insert the proper keys for any theme defined in D7 core files (includes and modules directories) as well as themes defined by the module being upgraded.
If there is a particular change from D6 to D7 that is important to contributed modules you maintain or use, consider giving a few hours of your time to help write and/or test an upgrade routine. Together, we can have our contributed modules ready for Drupal 7 when it is released.