There's a lot of talk about the potential of Mitchell Johnson and Shaun Tait. And while I agree that both have immense potential - Johnson more than Tait IMO - there's a lot to be said for the task at hand. The pressure on these bowlers will be immense because so many are expecting them to come into the side and impact immediately. Unreasonable expectations, and doubly so on Johnson because he's been so impressive in ODIs thus far.
It's true that the loss of both McGrath an Warne will hurt Australia greatly, but I hazzard to suggest that McGrath is the more critical loss. A bowler of McGrath's stature at the front of a bowling attack is so crucial. The only series that Australia has lost in recent times saw McGrath miss 2 Tests. England won those two Tests and established the margin of victory. And how many other Tests has Australia lost in recent times? Rhetorical, no doubt.
As Marc said, Clark seems capable of filling McGrath's shoes, but that still leaves two weak links in the seam attack, seeing as Brett Lee is still struggling to belong at Test level and there's need for a new 3rd seamer. So before even getting to the spin quotient of the attack, Australia have problems. I have no doubt that Australia will cope with these problems in time, given the impressive domestic structure they boast, but the weight upon young shoulders will be immense. Let's not forget that though Australia have unearthed Clark in the international set-up, he's been around for a while and, like Hussey, is no guarantee for the young talent that must come into the side.
Mitchell Johnson faces the toughest challenge of his career.