I'm in two minds about Brett Lee, next summer. No doubt his figures have improved markedly since his return from the Old Dart. Good on him - he's one of, from all reports, the most likeable guys in world cricket. However, I think it's an over-simplification to say that he has substantially improved since the Ashes series. The jury is still out, in my view. They'll return with a verdict after the Ashes. For not only do England represent a more potent threat, in terms of batting skill, than either South Africa or the West Indies, but they are an aggressive batting team.
Without doubt, against defensive teams, Lee is one of the best fast bowlers in the world. To give him his due, he's also been, on balance, the best ODI fast bowler from 2003 onwards. However, that he averages 44 with the ball against England in Test Matches is no mystery. They really attack his bowling. Not for them (unlike other skillful batsmen, such as Kallis last summer) sitting on him; letting him fall onto his preferred line and length; and counting the balls until the end of his spell. Instead, they'll attack him with everything they have, and put him under pressure; ask him questions.
He did bowl some withering spells in Ashes 2005. However, the reason why he averaged over 40 with the ball in that series was because, on the days when he wasn't at the top of his game, England did not let him settle - they made him react to them. Moreover, I just find it a little difficult to believe that a 29 year-old fast bowler has made such a dramatic improvement in the space of a few months. More likely, he has made a small improvement, but more significantly, out here in Australia and in South Africa last summer, he was confronted with defensive/less skillful batsmen who were unwilling to put the onus back on him.