Holy Shock is currently on a 15 second cooldown not 8, a 150% increase in output, although of course without a tabulated list I can't be sure ;).
Yes mana is a concern, but it's not like you're doing less damage than you would be with the slower cooldown, you can just thump it out faster. Mana use seems to be an engineered flaw of the build, particularly with the instaheal applying to Holy Light.
With Sheath of Light (if it doesnt get nerfed to 30% like it really, really should) and a healthy stack of spellcrit gear you could easily heal yourself with a combo of nukes and procced DoTs, be getting mana back from your crits, and still hit hard with SoR and Shock.
Edited, Jul 21st 2008 1:26pm by Sinstralis