With the new trinkets, the floor has fallen out of inferno ink. Admitidly on Alliance/Caelestrasz, it is cheaper than most, but at 26g per ink - in the middle of the darkmoon faire, it's price is heading south.
It's price is only going to get cheaper with the faire ending soon, as well as with the new trinkets from firelands. I see a few more runescrolls of fortitude II being made, and very cheap 359 trinkets heading our way.
On a somewhat related note, Blizzard are on record as saying "Yes. We will be changing the discovery spells so they can teach all possible glyphs, and the books will simply provide a no-cooldown method to do the same thing. "
At the moment, northrend inscription research is the 'major' discovery spell, requiring snowfall ink. If they leave the discovery spell using snowfall ink, once this gets implemented (patch 4.3? sooner? later?), Snowfall will become approximately equal to 10 Blackfallow ink in value, while Inferno becomes cheaper and cheaper, or possibly even drive some herbalists back to northrend.
I think that rather than encourage players back to northrend for grinding herbs, when Blizzard change the research spell to learn all glyphs, it will also change the ingredient to use Inferno ink; or possibly add a new research spell for Cata research.
Even with this possibility, I see dark days ahead for inferno ink