This is one of the most traditional ways to travel, and it provides for a nice alternative to the night bus if you need to get to Luang Prabang. There are a number of different operators which come with varying prices. We went with Shompoo Cruises, one of the mid range operators, with rather a garish colour scheme! The majority of the clientel made it look like it was a SAGA cruise, but the staff were knowledgeable and helpful.
You set off, and once the necessary papers have been filed, you are on your way. The first part of the cruise is very tranquil, taking in the beautiful jungle scenery and being mesmerized by the strange flow of the river. After lunch you stop at ... a small hillside village and visit a school, the kids are friendly and enjoy you being there. The evening is spent in Pakbeng, we stayed at The Sanctuary, which is not worth the money. Go out and explore the town, visit the market, grab some larb (local dish) and maybe have a drink or 2 at happy bar!
The next day you have 2 stops before Luang Prabang. The ... caves and the ... village. The caves host over 1000? Budda statues (check out our seperate blog on this). At ... village you'll get to learn about making rice whiskey and wander the market.
If you have the time, we'd recommend the slow boat, it isn't a busy itinerary, but the scenery is beautiful and it's a great chance to relax after the gibbon experience!