Having recently upgraded to an Apple notebook (woohoo!), I am learning the ins and outs of being mobile as I setup my new machine for work and for play.
One thing that was annoying was having to unplug my audio interface when I wanted to take my computer anywhere away from my desk.
On Saturday, I was sick in bed with time to finally work on some music. But, being in bed, I did not have my audio interface connected.
Usually that means that I would need to reassign all audio outputs in my sequencer to the built-in outputs to work on music. And change them all back when I wanted to work at my desk.
Not anymore. 
Soundflower is an OS X “system extension that allows applications to pass audio to other applications.” It presents itself as an audio device, and allows you to route audio from any application to any other application.
So, now I just set up my sequencer to output to Soundflower’s 2-channel device, and then from there to my audio interface. It’s simple to switch from the audio interface to the built-in outputs in Soundflower. I no longer need to re-assign the audio assignments in the sequencer.
There is a lot more that is possible with Soundflower. I haven’t played with the 16-channel device yet, but I thought that the convenience of the 2-channel device was worth writing about.
Soundflower is free and it works on Intel and PPC Macs.
info: http://www.cycling74.com/products/soundflower
download: http://www.cycling74.com/downloads/soundflower