Although the obvious uses of our new job ability are obvious, I haven't seen a dedicated thread yet discussing the finer details of Mana Wall. Pretty much everything can be found in the wiki article on Mana Wall, or should be added, but I figured it wouldn't hurt to share information here too.
Based on reports from others, Mana Wall appears to convert 2 damage taken to 1 MP lost. I'm not sure about which way this is rounded, but we should be able to test that. While that's not nearly as efficient as a cure or a drain, it makes the ability much more acceptable for general purpose use.
Mana Wall DOES convert damage from DoTs. It doesn't allow you to rest with a DoT on, but it also does not prevent the DoT from waking you if you're slept. This was particularly handy for me last night against Nightmare Sheep (Dynamis Valkurm), as I was able to use poison to keep myself awake AND have a defensive buff on.
Enmity: I haven't seen anything yet, but I'm hoping someone can point me to testing that has already been done. My two questions are: what enmity does the JA itself generate, and how much (if any) enmity do you lose when taking damage with your MP?