That agreement aims to replace existing bilateral agreements concluded by the US and individual member States after the Court of Justice handed down its judgments in Cases C-466/98 Commission v. United Kingdom, Case C-467/98 Commission v. Denmark, Case C-468/98 Commission v. Sweden, C-469/98 Commission v. Finland, C-472/98 Commission v. Luxembourg, C-475/98 Commission v. Austria and C-476/98 Commission v. Germany. The Court held that the bilateral agreements in question were contrary to EC law because their subject matter fell within the competence of the EC.
Rather disappointingly, the new agreement does not really aim to liberalize the provision of air transport services across the Atlantic and so will disappoint many travelers. It does not provide for the right to provide cabotage (a transport service between two points in the same country). The aim is more to provide for regulatory convergence on both sides of the Atlantic. There is a glimmer of hope that things will improve because the present agreement is a first stage and there is a commitment to a second round of negotiations.
The Commission has issued an "information note" giving some background to the agreement and summarizing its salient points. Real air transport boffins will enjoy reading this study of the economic impact of the agreement.
And while we are at it, here's the Council Decision on the signature and provisional application on the Agreement.