As Blizzard prepares to unleash Hearthstone's 'Goblins vs. Gnomes' expansion, there are still some housekeeping matters to sort out. Namely, there are some balance tweaks that need to be issued. A new round of changes is being made and it's mainly bad news for Warlocks that rely on their 'zoo' strategy and further puts a nail in the coffin of Miracle Rogues.
The biggest change is arguably Gadgetzan Auctioneer going from 5 mana to 6 mana. Given that Rogues often rely on their low-cost spells to draw nearly infinitely (often seeking out Leeroy Jenkins, who was given his own nerf previously), this deals a huge blow to those players. Gadgetzan Auctioneer is also utilized effectively by other classes, like Priest and Hunter.
Soulfire will also see an increased cost and will now cost 1 mana, instead of 0. Good Warlock players could often take advantage of the discard condition by emptying out their hands (often filled with minions) before using Soulfire to clear the board. This puts somewhat of a damper on that strategy, but doesn't necessarily kill it.
Finally, Hunters will see Flare's cost increase from 1 to 2 mana. Flare can mainly be used as an early play to draw an extra card, but it's also an extremely powerful card as it is the only spell in the game that can effectively nullify Secrets and also bring Stealth characters out in the open. It is an extremely underrated play and was a huge value at 1 mana. In fact, at 2 mana, it's still a pretty valuable card.
Check out the full details on these changes on the Hearthstone forums.