This is something I have learned on this trip. Don't be lazy. If you can get all your visas before you go, do it. Yes, even if it's supposed to be simple and they are giving them out like hotcakes at the border. Every border crossing we had was a headache in one way or another and it would have been lessened if we'd had our visas already set up.
For example, going from Saigon to Phnom Penh. A visa is supposed to cost $20 US but when we were on the bus they informed us that they charge $25 US so that they can speed us through the border. We were annoyed but didn't want to be left behind by our bus, like we were when we went to Laos and got our visa on arrival there. Then it turned out that at the ghetto border crossing (aka mountain hovel) where we came into Vietnam they had failed to give us a departure card. In most other countries this would have been no biggie. Just fill out another one, right? However, they are sticky in Vietnam and these cards are stamped on arrival to show where you entered the country. The bus guy said that they usually don't care if people lost them but it was our lucky day because they cared. So we had to stand there nervously and eventually they let us through but we had to bribe them. So there goes an extra $3 US/person. Getting into Cambodia cost us $16 US more than it should have. It was annoying and a little nerve wracking. Yes travelers, get your visas before your trip!