About the Artificer.

[Yael]

Can metamagic feats be applied to an infusion?

I don't have the source and thus cannot read it, but I've heard it and poked the curiosity.

[Karnith]

Yes, metamagic feats may be applied to infusions. Per the Eberron Campaign Setting:

Like a spellcaster, an artificer can apply metamagic feats he knows to his infusions. Like a sorcerer, an artificer can apply a metamagic feat to an infusion spontaneously, but doing this requires extra time. An artificer can craft alchemical items as though he were a spellcaster.