install MongoDB on OS X

install-mongo.md

download and un-tar

create db directory

mkdir -p /data/db

export mongo bin directory

export MONGO_BIN="/Users/lawless/Downloads/mongodb-osx-x86_64-1.0.1/bin"
export PATH="$PATH:$MONGO_BIN"

run mongo whenever you need to

mongod run

install the mongo gem from gemcutter

sudo gem install mongo

Thanks for this, the export paths was just what I was looking for.