(might as well continue my ramblings ...
I've discovered that gpe-announce is a program separate from gpe-calendar which displays a given message, plays an alarm (as long as /dev/mixer isn't currently locked by another process, that is) and prompts for dismissal or snooze time. If you snooze, it creates a file under /var/spool/at/ which is then picked up by atd at the appropriate time.
Running gpe-calendar from a terminal allowed me to see this message when I tried to set an alarm for an appointment on 2006-04-31 @ 1400:
/var/spool/at/1145646000.104-100: No such file or directory
Sure enough, that file doesn't exist. gpe-calendar also showed it's error message box about there being an at daemon problem, which previously led me to assume atd had died. I'd love to figure out what the file name has to do with the time of the alarm. UNIX time?
So it seems that gpe-calendar has problems creating alarms for future events(?). In any case, even if the file was created, /var/spool is a volatile filesystem which is recreated on each reboot, so they'd be lost. That should be added to /etc/default/volatiles/00_core & symlinked to a non-volatile placeholder.
enough for now. Stay tuned for more exciting updates