Took the JY Australia trip in October 2011 - my first JY holiday. All I can say is it was amazing and exceeded any expectations I had. We too had Sarah as a tour manager and she was great - she really looked after us and made sure we had all the details and any support we needed.
Australia was fabulous with so much to do - yes there are some early starts (03:30 in Cairns comes to mind) but it is well worth every moment with so many highligts - Sydney bridge climb, Ulura at sunset and sunrise, scubdoo diving on the Great Barrier Reef, a helicopter filght over the outback and just about everything else.
The group was great and everybody was very friendly and supportive so much that I loved the overall experience and went to China with JY in 2012 and have booked for Peru in 2013.
My overall advice - go and enjoy the holiday and I'm sure your travelling companions will be great.
Go and enjoy it - I certainly did !!!!!!