Another good venue is the Silicon Beach drinks - every Friday at 5pm at Bar 77 in the Grace Hotel on York St. 2-for-1 drinks , and you usually get a good cross-section of the Sydney start-up "scene" there.
(I hesitate to call it a start-up "scene" - after all, if it's a "scene", shouldn't it be glamorous? :-)
hey, i'm alex i'm also in sydney, if you'd like to talk, see some cool startupy things around sydney, etc. Just send me an email at alex@openondemand.com (goes to anybody else here as well)