Six days not enough.
Perfect weather - awesome mass transit - great people and culture. Six days and we barely scratched the surface (Zoo, St. Kilda Beaches, Queen Victoria Market, Luna Park, Warra River and Moomba festival, Fitzroy, etc.) Must head up great ocean road, try wine country, and maybe work in the ferry to Tasmanian next time.
Insider Tip:Awesome bikehare system with stations everywhere - most including helmets - and very cheap. Great app for download that shows stations, number of bikes, and number of open docks - as well as nearby 7-11s that carry $5 bike helmets. Check it out.