Hi Sarah (and anyone else),
I'd love your feedback on some different ideas for how to accomplish this. One thing we're considering is just letting you make an audience out of any other audiences. That would let you do any combination, but it might be hard to see exactly how an audience is made in one place.
The other thing we could do is let you do "included audiences" and "excluded audiences" on each experiment, just like in URL targeting. That wouldn't be as flexible, and you couldn't reuse the combination, but it might be simpler and easier to understand. Which one do you think would work better for you?
What about the possibilty to set an AND condition instead the default OR condition in the Experiment Audiences?
+1 to Frank,
He got there before me. I'd love to see the AND condition added to Audiences.