The 9.21 change notes
http://www.opera.com/docs/changelogs/mac/921/
say
Mac specific
PAC (Proxy Auto-Config) setting is now read from system.
I thought great! because I have several internet locations, one of
them uses a proxy the others don't, and opera didn't read the system
preferences. However, this doesn't actually seem to work - if I
uncheck the "use PAC" box in the network / proxy settings preferences,
opera doesn't connect to the internet. Safari and camino work as they
should.
Does the PAC thing work for anybody?
Sebastian