Multiple instances or one global?

[brian hook <bhook@...>]

This is an idiomatic usage question more than anything else.  I have a set 
of mission scripts for a game and I'm curious if most people use a single 
global Lua state or if they tend to instantiate multiple Lua states for 
parsing "one time" items.

I'm leaning towards using multiple instances, but was wondering if there 
are downfalls going in that direction.

Thanks,

Brian