Flex 4.5 to have size report

Flex SDK 4.5 will have a new option to summarize what contributes to the size of a swf file. use -size-report=<filename> in the compiler options (-size-report <filename> also works in Flash Builder) to generate a summary of the size of each type of data within the swf file.

There's more information at http://opensource.adobe.com/wiki/display/flexsdk/Size+Report