Since we are on the subject of spending money, many places which take credit cards can also charge in US$. This saves the 1-3% service charge most banks charge if your card is US based.
Most U.S. Visa and Mastercard issuers now charge you 3% of the U.S. dollar amount of the charge for any charges made outside the U.S.
As Mike pointed out your U.S. bank may well slap a surcharge on you for an ATM withdrawl outside of the U.S. However some banks and brokerage houses waive the fees for ATM usage in foreign countries. I know that Charles Schwab credits you for any fees for using their Debit card in any ATM worldwide.
If you use a Bank of America Debit card in an ATM outside the U.S. they will slap a surcharge on you. I believe it is a % of the U.S. dollar amount plus a small flat fee per usage.
Since I discovered that Schwab doesn't hit you with a surcharge that is the only card I use in ATMs outside the U.S.
Bank of America, Chase Bank and Charles Schwab have a daily withdrawal limit of $1000 on ATMs outside the U.S.
Even with the limitations of 1.5 million $RP at some ATMs you can usually run your card 2 or 3 times and end up with the equivalent of $330 or almost $500 U.S. for 5 minutes at the ATM. USD$500 will go a long way in Indonesia and the ATMs are all over the place. Occasionally we find one out of service or out of money but there are usually others around fairly close by.
There are one or two ATMs in Ubud where you can get $RP 2 million 2 or 3 times each time you run your card through the machine.
I have found that ATMs are much more convenient and easier than the hassle with exchanging money at a money changer where first of all you have to find one that is open, secondly he must have Rupiah at the time you are there, and finally you have to count it 2 or 3 times before you leave the counter to make sure that you weren't short changed.