Don't know if this is common knowledge...
If you get mana vamped DO NOT MEDITATE until your mana has recovered from the vamp.
If you meditate while reduced from a mana vamp you won't recover the mana that was sucked away.
I noticed this when I got vamped, looked at my mana and meditated. Mana went up fast from the med and I heard the "recover from a mana vamp" sound, but my mana didn't jump.... it just kept going up at my med rate.