I did (or attempted) the trip to Luang Prabang from the Thai border. The boat was a bit cramped, but the scenery was great. Unfortunately, 3 hours into it, the boat hit a rock with the propeller and we became stranded next to a village with exactly 4 huts. This being Laos, information was not forthcoming about when we might start moving, and what was provided was not terribly honest.

Eventually, I saw them pull off the badly bent propeller and start attempting to forge it anew in a fire on the beach, and that was when I knew we were there for the night (boats can't travel at night). It was a miserable, cramped, cold night on the boat. They ran out of food and clean water. I flagged down a speedboat the next morning and hopped on it with one of my friends. We paid a lot just to get on and avoid a bidding war and 2 other couples managed to get into this. The people on the boat had the nerve to scream repeatedly about getting out tickets from us so that they would get paid for our passage...we did not give them up.

Now, imagine a canoe hurtling down the river with a jet engine, a dodgy boat pilot, and two helmets for 6 passengers. Oh, and if you hit a rock, it's all over. It wasn't fun, it was expensive, but we finally made it to Luang Prabang.

The other people left managed to get to LP at nightfall the next day, many hours late. Given the lies coming from the boat managers, we had no idea when a "rescue boat" was coming.

So, the moral of the story is...check the water levels before attempting this. It could have ended up much worse. Also all promises about which boat you get or conditions or whatever are total lies.