Link to Elitistjerks forum for the theorycrafters among us:
http://elitistjerks.com/f31/t21280-inte ... afting_hq/
In short for the ones who cba to read it all, if you have more than 300 intellect, you'll gain regen in comparison to pre-2.4 , every priest should be hovering around (at least) 400/450 intellect raidbuffed with decent gear, so the expected regen increase should be noticeable.
Haven't done any numbercrunching, but 50mp/5 while casting is possible.
*edit: In general, for druids and priest +healing/spirit gems will now be better than healing/mp5 gems, that much is certain!
Let's see what it's like in practice tomorrow!