Well the Australia day long weekend brought gorgeous weather, and partner had been pestering me to try it out, so I finally did.
We rode into the city from home, and then along the Port Melbourne Tram Route Bike path to Port Melbourne. From there it's not far, through Westgate Park, to one of the termination points of the Westgate Punt, just under the bridge.
The Punt runs 10:00-5:00 Weekends and also on Public Holidays, and is $3 each way. On the day we went, there weren't many going over by the time we got there, but coming back we had to wait for two trips before we could fit! The pilot of the punt (if that's his correct title) said that he had never seen it that busy.
After crossing we rode on to Williamstown were we had a nice lunch, bit of a walk around before returning.
As mentioned previously it only runs on weekends, but with petrol prices the way they are, perhaps sometime soon it'll have to run 7 days a week! Apparently it may still be a threatened species however, so try it out while you have the chance. It would be a shame if it stopped running.
For further info, check out the Bicycle Victoria Page
As a cheap and cheerful day out activity if you are anything approaching a cyclist, this can't be beat for the novelty value of going under the Westgate Bridge, and also getting to see a part of Melbourne that not to many people bother with.