Hi Ian
Michael & Ben are right, Middle Harbour Yacht Club, just south of the spit bridge in Sydney, do have a register for crew looking for boats - in fact it is an official register, and you can phone the club and get on it. Then those of us who own a boat, can pick up spare crew when we need them.
In fact I own a boat moored at MHYC, it's a Sydney 32 called Jester (GBR 32), and we're looking for some more crew at the moment, for next seasons racing. We've not been sailing Jester a lot recently, as we chartered an Sb3 so we could do a little training before we went over to do the Worlds, which were in the UK this year. That's now over and we're back, and looking to get Jester out again in the spring.
So if you (or anyone else reading this post) is interested in racing then drop me a line, telling me how much experience you have.
MHYC race on a Wednesday afternoon (we don't sail that series), Thursday evening during day light savings (which we do) and most Saturdays (we will enter the point score series, which is about 3 races a month).
Good luck finding a boat.
cheers
Dave