After the press conference, Apple has already made available the new "Purchasing" functionality within iOS 4.xx and more specifically in the App Store application.
The latter allows you to find the complete history of applications downloaded from your Apple ID account and also distinguishes between applications downloaded and installed or not on your iDevice. Convenient when it comes to finding an application that had not managed to convince at first.
If you have been using an iPhone for a long time, this is where you will eventually realize the phenomenal amount of applications already downloaded;)
We talk about it on the forum.