Kalgan the lead developer has finally spoken concering paladins, and apparently the 50% illumination nerf may infact be too big a cut. Quoted directly he states...
Pally Community: I understand the illum nerf, but where did the 50% come from? It seems like a larger cut than needed!
Kalgan: Now that's a valid point. We're certainly keeping an eye on the 50% number.
Now some people on here have said that 50% mana return is how illumination is supposed to work, but clearly this may be incorrect. It would be nice to know however what Blizzard were actually aiming for when the nerf was proposed, as it would allow the pally community to work out what the correct amount should be.
For me personally i think the mana return should be somewhere between 60-75%, but I havent really looked at the mechanics of it yet with a raid level spell crit chance. Though it would also seem that it isnt the mana return percentage that is wrong, but rather the scaling of it based on crit chance. Obviously a paladin that has just acquired the talent is going to proc illumination a lot less than a fully geared up raid level healadin who would be getting 100% mana returns on every 4 heal casts (roughly).
The dependency I have on illumination has been getting stronger, purely based on the fact that the talent gets more and more powerful with every new healing piece I pick up.
However I do believe it will be a talent that will be knocked around quite a lot over the coming months. Healadins are currently in a nice position whereby they can marginally alter their gear to make up for the loss of mana return cased by the nerf. All they simply have to do is spend a coupla weeks getting mp5 or +healing and not focus on +spellcrit as much and they will soon be back on top of the pile. I myself have been finding such gear easy to pick up and currently have an mp5 of around 210.
On a final note, I find it odd how blizzard can master divine illumination so well, but find its 'part-time' counter part so difficult to perfect.