Thanks for the feedback, GG! Do you think preventing the Shard from reducing below a cost of 2 would be better? That way cards like Frogs couldn't be spammed as easily.
EDIT: Also, to address questions raised in chat:
It only affects cards in your hand AT THE TIME OF ACTIVATION. So, for example, you use SoI
(Roflcopter!), then use your Golden Hourglass to draw another card into your hand. That new drawn card would remain at its regular cost, without reduction. Unless you use another SoI afterwards.
Speaking of which, SoIs cannot "stack" effects. You can't spam four at once to get a 6
Bone Dragon, for example.
On bucky's suggestion (putting this here before I forget whose idea it was), SoI could cause an effect similar to that caused by Silence and Sanctuary, represented by the graphic. It would make it easier to see that the effect wears off after the turn it was played.