I found some JSON code that works pretty well - http://www.chipmunkav.com/downloads/Json.lua

I tried the JSON4Lua library first, but for some reason it crashes on the device (not in the simulator..)

JSON is a nice way to serialize your objects for saving. For example:

function readScores()
local path = system.pathForFile( "scores.txt", system.DocumentsDirectory )
-- io.open opens a file at path. returns nil if no file found
local file = io.open( path, "r" )

if file then
-- read all contents of file into a string
local contents = file:read( "*a" )
scoresList = Json.Decode(contents);

io.close( file )

end
end

function saveScores()

local path = system.pathForFile( "scores.txt", system.DocumentsDirectory )

-- create file b/c it doesn't exist yet
local file = io.open( path, "w" )

if file then
file:write( Json.Encode(scoresList) )
io.close( file )
end

end

It is also useful for communicating with web-based services.