We stayed here at the beginning of our trip around Southeast Asia and what a great start it was. We paid for the aircon room, which was well worth it in the February heat.
The price included free wi-fi and breakfast (with happy faces baked on to the toast!). So all up, great value. The bathrooms are shared, but were always clean and as it is not a large place, there are only a small number of guests sharing them.
The staff were exceptionally helpful, we were sent to a bus stop around the corner with written directions in English and Thai to ensure that we successfully arrived at Chatuchak market with minimal effort. They were friendly and welcoming and knowledgeable about local sights and activities.
Khaosan Baan Thai is a little hard to find if you don't know what you are looking for, we arrived by Tuktuk (From the nearest Skytrain station) and the driver had to ask around a bit once we got to Samsen Soi 3, it is tucked behind another guest house. Although it turns out that there are plenty of signs if you are looking for them!
The location is great, down a quiet street, but still close to plenty of interesting destinations. It is within walking distance of (among other things) the Grand Palace, Wat Pho, Khaosan Road, and several river taxi stops, so that you can quickly travel up and down the river, go on a canal tour or make your way across the river to Wat Arun.
The only downside about the location is that the area is not linked to the Skytrain, so you will have to take another form of transport to link to Bangkok's efficient Skytrain/underground train system if you want to go further afield.
When we were there it was quiet at night and we had a great night's sleep, but the rooms are not very soundproof, so if you were unlucky enough to have noisy neighbours, you may not sleep quite as well.
All up, a friendly, welcoming and relaxing place to stay, thanks guys!