CyanogenMOD team has started pushing out CM9 nightlies for Sony Xperia neo and Xperia arc smartphones. These nightlies can now be downloaded from here and installed via ClockworkMOD recovery.
Be sure to backup your smartphone contents or do a full nandroid backup in-case you want to revert to the existing ROM.
You will find the nightlies under the name Anzu for Xperia arc and Hallon for Xperia neo.
