Just finding out about this, but it seems that as of 4 October 2012, flag carrier Garuda Indonesia has been including the airport tax (Passenger Service Charge, or PSC) in the price of all domestic flights. That means that it’s no longer necessary to pay the departure tax at the airport, if you’re flying Garuda. Note that this only applies to domestic flights. According to an article in today’s Jakarta Post, implementation of the new scheme seems to be going well.
The article goes on to say that the scheme may be extended to other carriers and international flights in the future. Indonesia is almost the last country in Southeast Asia to still collect the PSC at the airport rather than letting the airlines collect it through ticket prices. Cambodia dropped it for international travelers last year.