From a virgin velocity email received today..
"Baggage Policy
On 16 May 2012, Virgin Australia will introduce a simpler domestic and international short haul checked baggage policy for Guests:
• Checked baggage allowances will be based on the number of pieces checked in rather than the total weight.
• A maximum of three pieces of baggage may be pre-purchased online or via the Guest Contact Centre at a discounted rate, including any complimentary allowances. Baggage may also be purchased at the airport at a higher rate.
• There will be a small flat fee for overweight baggage, rather than charging per kilogram for overweight baggage."
checked baggage http://www.virginaustralia.com/au/en/plan/baggage/piece-allowance/checked-baggage/
additional baggage costs
http://www.virginaustralia.com/au/en/plan/baggage/piece-allowance/additional-overweight-baggage-international-short-haul/