Required Packages 
 * bison
 * flex
 * git (git-core)
 * gperf
 * libncurses development headers (libncurses-dev)
 * make (build-essential)
 * mksquashfs (squashfs-tools)
 * openjdk
 * pngcrush - the build process will complain if it is not installed but builds will complete.
 * wget (or curl)
 * zlib development headers (zlib1g-dev)
 Warning 
 Do not build as root, always build as user.
 Setup 
Get and install the repo tool
{{{
 mkdir bin
 cd bin
 wget http://android.git.kernel.org/repo
 chmod a+x repo
 cd ..
}}}
Get replicant 2.2
{{{
 mkdir replicant-2.2
 cd replicant-2.2
 ../bin/repo init -u git://gitorious.org/replicant/manifest.git -b replicant-2.2
 ../bin/repo sync
}}}
 Each time you want to build replicant 2.2 
{{{
cd ~/replicant-2.2
 ../bin/repo sync
source build/envsetup.sh
export ANDROID_JAVA_HOME=$JAVA_HOME
lunch cyanogen_dream_sapphire-eng 
make -j$(echo "$(grep 'processor' /proc/cpuinfo | wc -l ) + 1" | bc) bacon  #uses arguments like -j9 to speed up build in case of multi-core cpu
}}}
Don't forget the bacon at the end, without that you will have some build errors.
Note that the bacon also produces standard images like system.img, just ship or use the system.img like images