We have been on a houseboat a couple of times now and think it is absolutely fantastic. We had a guide with us the second time and he was invaluable - we met some of the people who lived on the backwaters and had a drink with them, and visited local churches that you would never have known had existed.
As previously mentioned, the food is incredible. We managed to persuade the crew to eat with us and spent the evening chatting freely about the differences between our two lands, politics, religion etc.
I have not found anything to beat the experience of watching and listening to the dawn through a window 'flap' whilst lying on a bed.
The only downside is that the beds are barely big enough for one person, let alone 2, and if you have any part of your flesh up against the mozzie net you know it's going to get it!
Both myself and my OH go on holiday for experiences and 'moments' that flash back into our memories and the most frequent ones are of the houseboat trips.
Enjoy!