Today's release of the first alpha version of Drupal 7 motivated me to have a
deeper look at the code in order to start porting ThemeKey to Drupal 7.
I already know that the global variable $custom_theme doesn't exist anymore.
But if I look at the code, some patches that went into Drupal 7 and (most
important) the still pending patches in the issue queue it seems to me that
the corresponding feature in Drupal 7 is not ready yet.
What ThemeKey for Drupal 6 does is to set $custom_theme in it's implementation
of hook_init(). I already have an idea how to do something similar in Drupal
7. But is there a recommended or official way to that?