The micro-optimization introduced in http://drupal.org/node/646912 tries to detect for json_encode and, if present, introduces a local work-around to the 'setting' mode of drupal_add_js, by injecting a Drupal.settings variable through the 'inline' mode of drupal_add_js.
Using an inline insert for the Drupal.settings variable is problematic because it does not use the jQuery extend() function to add to Drupal.settings, which means that it could end up destroying instead of adding to the maps array. In addition, this isn't following the documented uses for drupal_add_js.
As it happens, I ran into this by trying to embed an openlayers map into a Dialog using the Dialog and CTools modules. CTools' AJAX rendering doesn't currently support the 'inline' mode from drupal_add_js, but it does have support for the 'setting' mode.
I think that it is better to use drupal_add_js as proscribed by the documentation and use the 'setting' mode for adding variables to Drupal.settings. If the concern is that drupal_to_js is too slow, that is where performance-concerned distributions like Pressflow come in. Pressflow, for what it's worth, switches to use json_encode in all places, so modules that properly implement drupal_add_js('setting') all benefit.
Attached is a patch against 6.x-2.x-dev that rolls back the json_encode detection and uses drupal_add_js properly.