PANIC, to me, is more of an agreement to gather and create collaborative art "live". Thus... you can PANIC on Gridcosm, HyGrid or Slithr. There are security issues with FTP that we haven't had time to work out yet. My plan has been to modify the Slithr scripts to allow for a more "open" image-series-style PANIC.
A suggestion I might make is to use the Collaborative Art club at Yahoo (SITO's only Yahoo club) to post images temporarily. Yahoo! Clubs collaborativeart <clubs.yahoo.com>
If anyone has a machine they'd like to set up an anonymous FTP directory on, that'd be even better.