I don't remember anyplace asking for $$ in hanoi

I have travelled around Thailand, Laos, Cambodia and Vietnam, having to change currencies as I went along. I didnt have any trouble at all. I would withdraw the maximum amount from the ATM in all of those countries, to avoid being charged each time (this is cheaper option but probably not the best carry so much). If you're carry so much money, just separate it out when you get to your hotel room. I have exchanged the left over cash from the previous country to the next, and had no trouble (even changing Vietnamese dong to Laos). Everywhere I went in Vietnam accepted VND, they never asked for US dollars except travel agents when booking trips. Most agents accepted VND but a few preferred VND. This trip was a year ago in 2012 so its fairly recent.

Most ATM's in Vietnam dispense US dollars, or VND, you can choose which one. I did have travelers cheques, but a small amount, and it was in Vietnam where I needed to use it. I couldn't cash it up at some banks and had to walk to the other side of town to cash it! So stick to credit cards and cash as its easier.

Whichever country you're in, DONT exchange at borders, airports or bus/train stations, you'll get a very poor rate and scam you as you're a tourist. I learnt that lesson myself.

Yes they do charge 150 Bhat at ATN, I was there in Jan and March 2012.