In an earlier version, unskilled Drain Mana did not break crowd control, whereas Improved Drain Mana did. This has been changed, so that it breaks CC regardless of this talent.
The damage caused by this talent draws extra aggro, which may be bothering.
It does not benefit from spell damage or Shadow damage.
Tips and Tactics
The extra damage bonus could be helpful, if a player used Drain Mana often. However, its damage is pretty weak and does not benefit from spell damage, making it less desirable for better geared players.
It is very important to note that this does not increase the mana given back by Drain Mana, it only adds a damage element. If you wanted to do damage while gaining mana, it may be more effective to use Drain Life in combination with Life Tap.
Patch 1.7.0 (13-Sep-2005): The Improved Drain Mana talent no longer does additional damage from plus damage items. This bonus damage was unintended and was a bug.