According to the Facebook event page (which appropriately labels the event type as a "slumber party"), the showdown will occur in Freedom Park on Saturday, Apr. 3. That gives you a full month to prepare, people. For instance, you can take the approach of the Facebook commenter who helpfully proclaimed, "Mine will be full of angry badgers!"
We also love the vaguely philosophical (erotic?) tone of the event listing:
Some groups have made the mistake of making their pillow fight last 15 minutes, or even worse, 5. It is best to estimate that the pillow fight will last an hour if you are pressed to select an end time.
Just wait until the pillow fight's natural end, when even the most stalwart soldiers grow weary.
See here for CL's coverage of last year's event and a video below detailing the carnage.