A chit-chat type interview with the former leader of Black Isle Studios (now Obsidian's head honcho) has been posted at E-Boredom. Here's a snip:

E-BOREDOM: Did the unique setting for Planescape: Torment offer some freedom for the designers?

FEARGUS URQUHART: The biggest freedom was that Planescape game setting was built upon the premise that thoughts could effect reality. So, the designers could explore a lot of ideas that were based on thoughts and emotions. It also helped that everyone felt that the world of Planescape was a more adult world - so things that might have been frowned upon in the Forgotten Realms was allowed to be in Planescape.

Click here (http://eboredom.20m.com/features/interviews/urquhart.html) for the whole truth.