now to actually answer the original poster's question...  :) 

On 7/13/05, Jeff Ellen <tgje underscore uiuc at yahoo dot com> wrote:
> 
> Does anyone know how much overhead m0n0wall uses?  For
> example, using m0n0wall as a bridge, how does
> throughput compare to having a simple switch or hub
> instead (with no m0n0wall at all)?
> 

As little (or as much) as any firewall.  Depends on too many things. 
With good hardware (or should I say sufficient hardware for whatever
load you're running) it's negligable.  In a very unscientific test on
a well loaded bridged firewall, somewhere in the neighborhood of a few
microseconds.  Nothing that's going to have any appreciable negative
effect on performance.

-Chris