It is well known that

  
If compiling takes even 15 seconds, programmers will get bored while the compiler runs and switch over to reading The Onion, which will suck them in and kill hours of productivity.

Our MonoTouch app takes 40 seconds to compile on Macbook Air in Debug/Simulator configuration.

We have about 10 assemblies in the solution.
We're also linking against some native libraries with gcc_flags.

I'm sure there are ways to optimize compilation time that I'm not aware of, which might have to do with references, linker, whatever.

I'm asking this question in hope that someone with better knowledge than me will compile (no pun intended) a list of tips and things to check to reduce MonoTouch compilation time for debug builds.

Please don't suggest hardware optimizations or optimizations not directly related to MonoTouch.