Someone else has just warned me off Jetstar so, as the only cheap flight tomorrow was with VirginBlue , I've booked with them.
$109 each way which given current fuel prices is not too bad.
Now I just need to check the baggage allowance and weigh the binoculars...
The last flight I took was to Perth (5 hours) so Sydney to Hobart (<2 hours) is just a stroll 
I don't know how people can manage the length of overseas trips. Perhaps the free alcohol helps ...