I tend to agree with Kein-Hong Man's main Lua-related point: your typical public probably has a pretty specific kind of issue: big systems, gluing together legacy bits of code, etc. The most appropriate kind of success story you might be interested in is Mark Hamburg's, and it's pretty well summarized here:
http://www.lua.org/wshop05/Hamburg.pdf.
Basically, about half of Abode's Photoshop Lightroom code has been written in Lua, and they seem extremely satisfied with the result. He exposes in his slides many of the generalizable benefits they enjoyed from picking Lua & C++ as Lightroom's implementation languages.
-- Fabien.
