Scripting language usage

I''m curious how extensively the people here use scripting languages within their game or engine. By this I mean languages that can be easily edited or modded, as opposed to the C++ or whatever that the actual engine is made of. My only real experience in this regard is with the Quake3 engine, which contains a core engine, but all gameplay is done by "script", easily replacable C programs that compile to byte-code. This allows for a lot of customization, and things like Total Conversions, but I''m sure there are risks involved as well, and speed issues. The same seems to be true for the Unreal engine, but on a more sophisticated level, using a very complex script language and allowing multiple mods to co-exist. For my game engine I''m still undecided how much I should code into the engine, and how much I should expose through a script language and just leave for the game to implement. What are the different levels of scripting that people use? I don''t like the idea of creating a minimal engine skeleton and leaving it to the script to do the entire game, but I also don''t want to make the engine hard-coded to a single gametype. I''m just looking for examples to get a bigger impression of the possibilities.