Like Colin, I too live in Australia and took out Australian Citizenship.
Enrolment on the Electoral Roll for all Australians over the age of 18 is compulsory.....VOTING IS NOT COMPULSORY......all that is required by LAW is that you attend a Polling Station and have your name ticked off the Roll as having attended.........YOU ARE NOT REQUIRED TO CAST A BALLOT.
To answer Sheilas question about keeping UK Citizenship...........it will cost $197.00 ( at last time of asking) to renounce UK Citizenship........ I cannot see the pint of paying to say ""I don't want you any longer""........Eventually the Australian Republican Movement will succeed and this will occur without cost.