I booked and paid in advance through Lao Airlines which turned out to be a rip-off, as the agency charged me double the walk-in rate and there were plenty of vacancies. Also, your advance payment paper does not mean the guesthouse has already been paid when you arrive. It just means they can collect from the booking agency - and this sometimes takes quite awhile. So neither I nor the owner was happy with this advance reservation.
I don't recommend Lao Airlines reservation arm - their computers seemed to break down, it was hard to get a response, and they did not seem to understand much English. I thought their mark-up fee was way too high.
Muang Ngoi does not have 24-hr electricity yet so unless the guesthouse advertises "hot water showers" (which means they use propane to heat water), you have to depend on solar heat and a few hours of deisel-generated power in the evening. Ning Ning relied on solar, and since it was cloudy for two of the three days I was there, there was not even lukewarm water. One evening there was no water at all for a few hours. The "heated" water seems to come from a centralized tank and you have to run the tap for up to ten minutes to get it to reach you. When I complained they moved me to another bungalow that supposedly had faster access to warm water.
There was just enough deisel-generated power for three hours in the evening for me to charge up my camera battery, my Kindle reader, and my netbook computer. And of course there's no internet in town.
The Ning NIng compound is near the top of the steps up from the boat landing. The woven wall and wood bungalows were very simple but adequate. There were cracks between the floor boards that would provide access to mosquitoes in the rainy season, but I did not notice any bugs.
The eating terrace extends over the riverbank looking down at the boat landing, with fabulous views to either side. The menu was varied and the food quite good. The cooking is done using big propane tanks for fuel in the kitchen underneath the eating terrace. It was a real pleasure to eat while watching the activity at the boat landing, the morning mist on the dramatic green mountains, or the sunset on the river.
Bring your earplugs as the roosters seem to have insomnia and can sometimes crow at all hours of the night, along with the barking village dogs. It is very very dark when the deisel power shuts off about 9:30 p.m. so a flashlight is handy.
There was a nice thick duvet on the bed - very cozy as temperatures can be pretty cool overnight and early in the morning in that northern location.
You can hike to outlying hamlets on your own along a pretty path that follows a small river. The main street of Muang Ngoi ( a dirt road) offers quite a variety of eating opportunitites including outdoor dinner buffets and even an Indian restaurant. There's an excellent massage place about half way along.
If I was doing it again I would not book in advance, but hope to get a room in one of the places that have signs for "hot water shower".
That said, the friendly manager and his wife were apologetic about the water problems and run a clean efficient place. They said that ten years ago everyone was a subsistence farmer and now there must be 20 guesthouses along the river. A road is being constructed to the village, and that will spell the end of the wonderful boat trip from Nong Khiaw.