Use SpringSource Tool Suite (Version: 2.3.2.RELEASE, Eclipse 3.5) with Flex Builder 3 Plug-in:

• Install Flex Builder 3 Plug-in
• Choose Flex install folder
• Use folder “sts-2.3.2.RELEASE” with STS executable and install despite the advices
• Modify file “com.adobe.flexbuilder.feature.core.link” in links directory of SpringSource and update it to:
  
  “path={Path to install folder}/Flex Builder 3 Plug-in”

It works with Eclipse 3.5 too.

Flex application compiling delay big projects development. Every change we make on shared libraries as a projects or .swc files linked to the main project it have to be re-compiled and invest time in this operation.

A solution to avoid that is to add the library as a new data source folder external in the project.

Installation Error in Flex Builder 3 plug-in for eclipse in Windows: