Nobody uses it, and for good reason; its activation trigger and its ability are at cross odds with each other. The low cost, extra cards, and requirement that you have few-to-no allies in play screams that this is designed for the opening hand to speed up a deck. (Heck, just look at the card's name!) But in a standard 3-hero deck, at least 50% of the cards will need to cost 3+ resources just to make Taking Initiative self-replacing, and you'll probably want at least 2/3s costing 3+ just to feel like it's turning a reliable profit. Which means unless you're playing mono-leadership, a strong majority of the cards in your deck will be completely unplayable on turn 1. In short, this is a speedy card that only plays in glacial decks, and is generally useless starting on turn 2.
There are a couple of ways to "trick" this card into usability. Two-hero decks lower the cost requirement. Secrecy cards have a much higher printed cost than functional cost, meaning you can get the benefit of triggering Taking Initiative without completely forsaking early-game playability. Those two factors, (two hero decks and secrecy), go together like peanut butter and jelly, so with a lot of massaging you can make this work. You're still going to need a lot of other card draw to make sure you're getting your Taking Initiatives in hand before you start playing allies, and of course most card draw is cheap enough that Taking Initiative will fizzle if that's what it flips. So it's a tough tightrope to walk.
Is it worth it? When Taking Initiative hits, it's a thing of beauty- think Deep Knowledge, except instead of having to raise your threat by two, you get to deal two damage to any enemy on the board. Except card draw's power grows geometrically, as each additional piece increases the odds that you draw into another piece and continue the cycle. In a 2-hero deck with Taking Initiative, Daeron's Runes, Deep Knowledge, and possibly the Seeing-Stone (with every other card costing 2 or more), it would not be the slightest bit uncommon to see 15 or more cards in your first planning phase... and likely take yourself out of secrecy range in the process.
At the end of the day, just a poorly-designed card that sounds really fun in theory, but is rarely going to be worth even a fraction of the effort required.