allow the author himself to select a theme for all his nodes

I totally forgot about this thread :) But the other thread I created still stands

So is it not currently possible to create a module or addition that would do this in combination with themekey?

Basically:
1.) User selects themekey setting in profile
2.) Helper module creates new themekey rule for selected user/theme
3.) All users now see the author's selected theme when viewing that author's content

What I'm thinking of doing is creating a small module to provide a new tab and form in the user profile, that lists the available themes on the site with checkboxes for the users to select from. What I'm trying to figure out is how I should update the themekey_properties table. I found the function for themekey_rule_set - can/should I use this vs. updating the table directly? In my configuration, there would only be one rule per UID, so it seems like I could just update the table directly myself

Then again, I'm not a programmer, so maybe I'm missing something important :)

Wow, that was some quick work - I'll be back where I can test this out in a couple hours, so I will check this out ASAP for feedback and more :)

I was able to successfully patch and update my themekey module, enable the user interface option, and select the new theme for a test user. I tested with both the admin account and a sub user account, swapping themes multiple times and checking the view from each account.

When viewing that user's content, the theme changed as expected. Very nice work :)

I'll put together something tomorrow with some screenshots. There is some wording that needs to be fixed in admin interface

Under admin/settings/themekey/settings/ui, the help text for the checkbox "Show theme option in user profile" should say something like "Assign themes from user profile. This will show a 'Theme' section under "edit" in user profiles.

Currently it says same as create/edit node forms.

Something else I noticed was if a user selects a theme, and then you disable the theme in theme selection - the disabled theme is still shown for that user's content. That's not a problem for my functionality, but thought I would mention it in case it should behave differently (like defaulting to main theme)

Wasn't sure what format you wanted me to give you the tutorial in, but I just pasted this into my themekey_help.inc based on your existing tutorial example. Images attached in this post

  $form['themekey_help_tutorials']['Allowing users to select a theme for content they create'] = array(
    '#type' => 'fieldset',
    '#title' => t('Allowing users to select a theme for content they create'),
    '#collapsible' => TRUE,
    '#collapsed' => $form['themekey_help_tutorials']['#collapsed'],
  );

  $form['themekey_help_tutorials']['Allowing users to select a theme for content they create']['item'] = array(
    '#type' => 'item',
    '#value' =>
'<p>' . t('In this tutorial you will learn how to enable users to select a theme for content they create.  For example, if you would like each of your bloggers to display their own theme on each of their blog entries, this tutorial will allow you to grant this option.</p>') .
'<p>' . t('First, you must enable any themes you would like available from under ').l('admin/build/themes','admin/build/themes').t(' (Administer -> Site Building -> Themes)</p>') . 
'<p>' . t('Once you have enabled your themes, navigate to ').l('admin/settings/themekey/settings/ui', 'admin/settings/themekey/settings/ui').t(' (Administer -> Site Configuration -> Themekey -> Settings -> User Interface). You will see a checkbox for "Show theme option in user profile".  Click on the checkbox and save your settings.</p>').
'<p>' . '<img src="' . $img_path . 'themekey_user_profiles_2.png" alt="' . t('Enabling theme selection in user profiles') . '" style="border:solid #d4e7f3 2px;" /></p>' .
'<p>' . t('Next, you must grant permission to the roles that you would like to be able to change themes for their own content.  Navigate to ').l('admin/user/permissions','admin/user/permissions').t(' (Administer -> User Management -> Permissions) and check the boxes for "Assign theme to own nodes" to all roles you want to enable this option.</p>') . '<br />' .
'<p>' . '<img src="' . $img_path . 'themekey_user_profiles_3.png" alt="' . t('Enable correct permissions to use themekey for your users') . '" style="border:solid #d4e7f3 2px;" /></p>' .
'<p>' . t('Once you have done this, your users can log in, navigate to My Account -> Edit and a new option will appear under their account settings.  A full select list of your enabled themes will appear for them to select from.  Once they have chosen a new theme, any node that is authored by this user will display the theme they have selected. </p> ') . 
'<p>' . '<img src="' . $img_path . 'themekey_user_profiles_4.png" alt="' . t('ThemeKey rule chain that switches to different themes on content creation forms for different user roles') . '" style="border:solid #d4e7f3 2px;" /></p>' .
'<p>' . t('Have Fun!') . '</p>',
    );

?>

Missed the third image attachment in the previous post

Coming back to this post after a while :)

I've noticed that in the account area, if you have multiple pages under "edit" that are added by other modules (for example, I have a billing module that has an additional page there), then the selection fieldset for themekey shows up in these other pages as well

It's a small detail, certainly not critical, but thought I would point it out :)