The morning that we took the first of our two 8-hour long slowboats, I woke up and immediately projectile vomited all my last nights curry into our toilet. Yuck. So I wasn't feeling all too great about the prospect of a long boat journey, but it actually turned out to be really relaxing. You could read and write in your journal and walk around which you can't do on buses, and the scenery you pass through is insanely beautiful (though a bit samey after a while). We stopped off overnight at Pakbeng village and the boat we took on the second day was built to carry cargo so didn't have seats and you just had to find a space on the floor. It was pretty much 2 days of blissful nothing, just lying in a boat, reading, talking, playing cards with people, admiring the countryside/riverside landscape. Definitely worthwhile, but definitely not the "once-in-a-lifetime experiences" that the book makes it out to be.