This has been touched on a couple of times, but another one I’ve discovered is that the machines in Laos (well, the one in Vientiane that takes foreign ATM cards) charge 20,000 Kip ($2) per withdrawal. This is in addition to any charges your own bank levies.
The single ATM in Vang Vieng will only work with MasterCard and I have been told that the one in Luang Prabang will only accept one of the more obscure card “brands” (i.e. not Visa or MasterCard).