Here's a quick run-down on organising your cash for a trip to Burma.
Yep, there are now ATMs in Myanmar (Burma), as every traveller has undoubtedly heard. There are plenty of ATMs in big towns (Mandalay, Yangon) and the most touristy destinations (Bagan, Inle). But it's not smooth sailing yet.
Power cuts are still pretty common, so it would be unwise to completely rely on ATMs.
Because of international sanctions, some western banks refuse to allow transactions to go into or out of Burma. Which means that your bank card or credit card will be rejected by that shiny new ATM, as your home back or credit card issuer refuses the transaction.
In the UK, both Halifax and Santander take this position. I can't speak about other banks, but I wouldn't be at all surprised. They also might not remember to tell you: I called Santander (my main bank) a few days before I left for Burma to let them know I'd be abroad (so they didn't stop my card fearing fraud the first time I tried to use it out of the country) and they registered my trip on their system without saying a word. I only found out later that they blocked all transactions in Myanmar.
The lesson here is: call your bank and ask this question specifically before you go.
If your bank doesn't allow you to use ATMs, you'll need to carry with you enough cash for the entire trip, which leads me to:
US cash and changing money
That thing you've heard about US dollars being pristine? Yes and no. For large bills it's true. For smaller bills, not so much.
Money changers normally have 3 different rates posted: one for 50 and 100 dollar bills (the best rate), one for 20 dollar bills, and one for 1 and 5 bills (the worst rate). 10 seemed to mostly be lumped in with 20, but in a few places I saw it included in the lowest rate with 1 and 5.
I never tried to change anything below a 50, but believe me, they check those 50s very carefully to ensure they were pristine.
20 dollar bills also need to be kept in good condition (I had one creased 20 rejected by a hotelier).
Creased 1 or 5 dollar bills are fine - no one seems to care if they're not pristine.
For hotels, you can pay in kyat but the rate's not good (when I was there, the exchange rate was about 960-970 kyat per dollar, and hotels will except 1000 kyat in place of 1 US dollar) so pay in dollars where possible.
Try and keep a mix of bills of various denominations so you can pay in exact cash, or close to it (so try and avoid paying a 20 dollar hotel charge with a 50 bill), at least until the last few days of your trip. This is mostly because they will often try and give you creased dollars back in your change, and like I said above, if it's a 20 you'll have trouble using it in Burma. Once you leave the country, of course, it will be usable again, which is why I don't mind accepting damaged notes at the end of the trip.
For hotel extras (paying for mini bar, bike rental, bus tickets they booked for you, etc.), expect them to prefer payment in kyat, rather than dollars.
Government owned tourist fees (the entry fee to Bagan, Inle Lake, or the big Yangon pagodas) can be paid in either dollars or kyat, again at the poor exchange rate of 1000 kyat = 1 US dollar.
For all your other day-to-day costs (taxis, buses, meals, drinks) you'll be paying in kyat. Most of the time they locals won't want to accept US dollars, nor will they necessarily have much change available, so ensure you've got a supply of small kyat notes on you. I found bigger shops and more touristy restaurants normally had a good amount of change available, so I'd use my 5000 or 10000 kyat notes (that I got from the money changers) there, and keep the 100-1000 kyat notes for paying at small shops and street vendors.