Never in recent tennis history have I seen a top four so strong, and it only seems to be getting stronger. Djokovic may not be as invincible as he was last year, but he's still pretty close to that level. Nadal is still as lethal as ever, as shown by AO, and is still virtually dominant over everyone on tour besides Novak. Murray seems to finally broken into to the Djokovic/Fed/Nadal triangle, with victories over Nadal and Djokovic in recent months. He also seems to finally be handling himself like a true great player on court. And last but not least Federer is playing his best in the past couple years, being nearly untouchable since last years USO. Not even the usual candidates for upsets like Tsonga, Berdych or Del Potro are giving these guys any trouble recently. They really all seem to have hit a run of form at the same time.