Maybe this has been addressed before but the only thing I remember from the conversation regarding this ability's usage is that people seemed to think it would work. The trick, as many of you probably know, goes as follows...
You combine psycarnum infusion with midnight metamagic in order to apply a metamagic feat you have to a spell you have prepared for free as long as that metamagic feat adjustment is <= whatever the essentia capacity of your midnight metamagic feat is.
I have a problem with this due to the specific wording of the feat.
Midnight Metamagic
( Magic of Incarnum, p. 39)
[Incarnum]
You can channel incarnum to alter your prepared spells. When you cast such a spell, your hands gleam with a dark blue radiance.
Prerequisite
CON 13, ability to cast 1st-level spells, any metamagic feat,
Benefit
Once per day, you can invest essentia into this feat and choose one or more spells that you know (and have prepared, if you prepare spells) to apply the effect of a metamagic feat that you know. Each spell to be affected requires the investment of a number of essentia equal to the normal spell level adjustment required by the metamagic feat (minimum 1 point of essentia). The next time you cast that spell, the spell gains the effect of that metamagic feat without any change to its level (or casting time, if you cast spells spontaneously). You can apply the effect of this feat to as many spells as you can afford to invest with essentia. You can apply the effect of different metamagic feats to different spells, as long as you know all metamagic feats applied and you have suffi cient essentia capacity to do so. For example, you could invest 1 point of essentia to enlarge a spell (as Enlarge Spell) and 2 points of essentia to empower a spell (as Empower Spell), as long as you had at least 3 points of essentia to invest, had an essentia capacity (see Table 2-1: Essentia Capacity) of 3 or greater, and knew both the Empower Spell and Enlarge Spell feats. Once essentia is invested in a spell, it remains invested until the spell is cast, at which point the essentia returns to your essentia pool. You gain 1 point of essentia.
It seems to me that people are using the trick to essentially apply any metamagic feat they want on the fly to any spell they are casting but the wording of the feat itself appears to imply that you would be unable to do this.
Once per day, you can invest essentia into this feat and choose one or more spells that you know (and have prepared, if you prepare spells) to apply the effect of a metamagic feat that you know.
Notice the once per day stipulation which applies not only to the time-frame one is able to apply essentia to the feat (which psycarnum infusion gets around), but also to the choosing of spells that are to be modified with this feat (which psycarnum infusion does not circumvent). The way I read this is that you can only
once per day choose a spell(s) to be modified with this feat and you would be unable to do this on the fly each time you use psycarnum infusion.
This is unlike the power point recharge method using Azure Talent.
Azure Talent
( Magic of Incarnum, p. 34)
[Incarnum, Psionic]
The soul energy of incarnum increases your mental capacity.
Prerequisite
CON 13, a power point reserve,
Benefit
Once per day, you can invest essentia into this feat. You gain bonus power points equal to twice the invested essentia. Once the amount of essentia invested is chosen, it cannot be altered and remains invested for 24 hours. If you have the ability to bind a soulmeld to your crown chakra (even if you don't have one currently bound), you gain an additional 2 bonus power points as long as at least 1 point of essentia is invested in this feat. You gain 1 point of essentia.
In this case, just as with all of these feats you can only once per day invest essentia (which psycarnum infusion circumvents), but unlike midnight metamagic, the static effect of this feat,
You gain bonus power points equal to twice the invested essentia.
is its own clause, separate from any once per day stipulation. Therefore, as it is known, each time you use psycarnum infusion to invest essentia into this feat it would obtain a fresh pool of temporary pp equal to the essentia capacity.
Am I just dredging up an old argument here that I was unaware of, or have I basically proven that any psycarnum infusion/midnight metamagic cheese basically doesn't work by RAW or even RAI?