+ symlinking my 5.1 folder of Lua modules to where LuaJIT was looking for them.
In terms of performance, they have a nice page here that shows how well it goes on algorithms: http://luajit.org/performance.html
On 'normal' usage of walking around and etc with a full curing system, I actually didn't notice much of an improvement looking at the s: meter - maybe 20% or so, hard to eyeball it since it jumps around here and there for such miniscule amounts (didn't help that I have CPU powersaving on so it'd clock the CPU from 2.2ghz to 800mhz as it wished).
Though, it'd be good to include in Mudlet starting with 1.3.0 or so since every bit does count.