So far, I have a few ideas for weekend trips: 
1. Mexico City for this amazing exhibit
2. A visit to Palenque! Fellow Oaxaca NEHer Pearl and I are hatching a plan to bus it there... awesome! 
3. Beach and snorkeling
OK, off to start reading... Stay tuned.
Oh, here's the group blog, in case you're interested: http://nehoaxacasummerinstitute.blogspot.com/