Since v 1.3.2.0 beta we added additional swc file to the package of our Flex components – amChartsFB4.swc. This file was compiled for use with Flash Builder 4 (aka Gumbo) – enjoy!
Note, because of naming conflict style “depth” was changed to “depth3D” in this version (both in Flex 3 and Flash Builder 4 components). So if your charts were 3D, you should change this style name in your applications.