I run Flex Builder 3 on a mac and as my project grows - the compile time gets longer and longer and longer. I am using some SWC\'s and there is a fair amount of code but it
I don't use Flex Builder, but I use the Flex SDK compiler everyday and I was wasting tons of time waiting for the MXMLC compiler to do its job until I found Flex Compiler SHell:
http://blog.zarate.tv/2008/12/07/theres-something-called-flex-compiler-shell/
Although in theory Flex Builder already uses this optimizations, might be worth checking.