CyanogenMod 9 has become officially stable for the GSM Galaxy nexus (Maguro). This means that the team has deemed this ROM pretty much bug free. Their standard for stable is very very high, so you know what this means.
However, I don’t quite see a reason to ever flash it. After using a Galaxy Nexus with Jelly Bean, I don’t think CM9 could ever be an option again. Project Butter on the GNnex ruined my Galaxy S II for me, and going back to ICS would just be impossible. That’s just me though.
Hit the source link for the ROM download, and be sure to seed it (it’s a torrent).