Are they selling daily passes, or could you still get in paying the coverage charge at the door for whatever gig is going on?
not daily passes...no. they sell individual tickets for individual venues for the night. get the tickets early. seriously. pick one venue for the night, get there before they open, and get your ticket. don't plan to go anywhere else that night, because chances are that you will fail, and failing is something at which few of us need more practice.
also, you can fill your day going to free shows all around town, get nice and drunk, see lots of music, keep your wallet happy, and go do something less filled with self-important industry blow-hards (and i mean that in the nicest possible way...) in the evenings.
for example, i'm going to see willie nelson at the backyard on saturday intead of even messing with sxsw.