Remember that the classes you are taking, you might be giving in a few years.
Seriously.
Some of my first teaching jobs were for classes that I took in my opening year or two of grad school.
Take notes on how the class is being given. Grab extra syllabi. Grab a spare copy of every assignment. GRAB EVERYTHING!!
Also recognize that you are in class with someone who may eventually be on your committee, may write you a rec, may have a contact for a job, etc...
If it helps you any, remember that Sweetwater will soon be out with its DonkeyPunch barleywine.
Cheers,
Lavabe