When I started at UNSW I didn't go to O Week, and I guess that must have scarred me for life. Tales of all-night booze ups, predatory behaviour and insane yellow shirts in jumping castles only come second-hand to me. Anyway, I found it wryly amusing that CSU has disallowed the political parties from having stalls. Back in my day, it was the Christians that clashed with the powers which protect the youth from sullied minds.
Circa 1994 or 1995, Campus Bible Study (CBS) wasn't registered with CASOC (the Guild's Clubs and Societies coordination and funding committee) for reasons unbeknownst to me, and so some wags got together to register CBS, the Children Born of Satan, inaugurating their club by sacrificing a watermelon on the Quad lawn. The O Week rules were that only CASOC-registered clubs can approach the mobs of first years and solicit their membership, and there was a lot of rumbling about the lack of teeth in CASOC's response to the unofficial CBS, whose actions were deemed predatory and unseemly by many. (I grant there may have been some anti-Christian sentiment in all that, but some rules were violated as I recall.)
Anyway, this got resolved some time in the late 90s when the officially registered CBS folded and the CBS as we know and love it got CASOC approval to do what the hell they wanted during O Week.
(By all means correct my faulty memory in the comments.)
... and it seems the answer to whether Sydney Uni has an O-Week is now a definite yes (whatever it was before).