The new mage items are really good on supports
Particularly
Supports with heals and shields who have the damage to generate blood charges (

) can pump out crazy healing in teamfights with an
.
It has potential on
, but they have individual problems. Soraka and Janna may not deal enough damage to make the most of blood charges, Bard doesn't like buying mana regen, and I don't know how it interacts with the AOE healing from Alistar.
massively enhances the pick/engage potential for many supports.
can all benefit from this (not all of those are supports, I know, but they CAN play support).
is good on
. Why? It is an item that gives decent HP, mana, and AP as well as an active that is kick ass for peeling. The reason to buy this over some other AP item is the new catalyst passive. Look at her mana costs lategame. 150 on Q, 80 on W, 110 on E, and 100 on R. This translates to 25 hp back from casting Q, 20 hp for casting W, 25 from casting E, and 25 from R, on lategame cooldowns of 5.5 seconds, 6.6 seconds, 5.5 seconds, and 66 seconds respectively.
You thought Janna was annoying to kill before? Now that she can get HP back on every spell cast, that is gonig to be even harder.