Application Express 4.0.2 was released on November 19, 2010. It addressed most of the known issues with 4.0.1. 4.0.2 is a cumulative patch - meaning it includes all the fixed from 4.0.1 as well as 4.0.2. If you followed any workarounds in your code, those can be removed after applying the 4.0.2 patchset.
Below is a list of existing known issues with 4.0.1.
This page was last updated on 19-Nov-2010.