Is it true that the Cambodian Riel is rarely seen in Cambodia and that the dollar is more popular? Is it worth taking $100 with me even though Im going to Thailand for a month first? I thought it might be useful to pay for the Visa. What do cash machines despense?
The Riel is used for small purchases such as bottles of water, taxis etc, and the dollar is generally used for accommodation and meals and other larger purchases.
I used a cash machine in Siem Riep that dispensed US$, but not sure how widespread this is across Cambodia. Remember to change any Riel back before you leave Cambodia as you won't be able to once you leave the country.
I just got back from Cambodia a week ago, and they use a mixture of US dollars and riel. Pretty much everyplace we went to accepted both, and it's possible to pay using a combination of both (most places worked on 4,000 riel = US$1). Pretty sure you will need US$ for your visa if you are getting it at the border though.
It's handy to have some small change in riel for the markets, and for buying small things like Bec said. I withdrew money from ATMs in both Phnom Penh and Siem Reap and they dispensed US$. I can't remember seeing any ATMs that dispense riel.
If I was you I'd just get US$, because as soon as you start buying things you're likely to get some riel back in change anyway.