I worked for AUA's main branch at Rajdamri, and although I stayed there for only 2 months (I had a can't-refuse offer in China, still there) I really have some pleasant memories of the place, and nothing but good to say about my stay there.
First, before you get bored with my details and move on -- let me say it's a real pleasure to be able to work with students other than the very richest kids in Bangkok. AUA at the time charged students something like 1200 baht for a 30 hour course -- ridiculously low by Bangkok standards (which goes a long way towards explaining the somewhat dismal hourly rate). This means that you get to teach students from all walks of life, not just the rich kids whose parents are trying to send them abroad. I found this mix of middle-class students to be very hard working and the teaching more fun than work. Two years later, I still keep in touch with several students. Not trying to slam or generalize the Bangkok elite, but I felt I was treated with respect as a teacher by the students there, not as another member of the hired help. My students were composed of everything from high-schoolers to young business managers, secretaries to ex-bargirls, even a few non-Thais, Koreans and Russians who'd come there for the bargain basement prices.
Although I was qualified and experienced, I was assigned a mentor who was to spend and hour a day with me for the first month. I was paid for this hour (so I taught 3 hours a night, paid for 4) and the mentor was cool and very laid back - spent most of the time showing me around the place and letting me know where all the materials were. I was given all the necessary books and materials, including teacher's guides, and AUA-specific teachers guides, which pretty much walked you through the lesson step-by-step.
They have a dozen filing cabinets full of photocopies of everything you need for class -- go to the appropriate level and week, and voila - everything you need, copied and ready to go. If you have something of your own you want to add, you've got to show up a bit early and get someone to sign off on it, but if they feel it's valuable, they'll make copies and put it in the file -- so you only have to do this the first time. After a few weeks, preparation time dwindles down to almost zero.
The facilities, though a little aged, are excellent. Entering the building is like going into a high-school campus, with a canteen, coffee shop -- lots of relaxed opportunities to interact with the students. If you're interested in socializing a bit with the students outside the classroom, there are lots of opportunites, as the students show up a bit early for coffee or even dinner at the canteen.
Yes, working five days a week will net you 20-24k a month -- but you're only working from 5pm to 9pm everyday, which goes by very quickly. I wasn't there long enough to get into the Saturday classes, which start every quarter, but every new teacher is required to sign up for the first 2 available quarters - after that it's optional. However, Saturdays pays more than double the hourly weekday rate, and if you want to work 6 hours on Sat, you can get your pay into the 35-40k range.
Mon-Fri classes run 6 weeks at a time, with a week's holiday in-between. Towards the end of your contract, you can sit out one of these 6 week courses if you need a longer holiday. Now, both the week and six week breaks are without pay, but if you're coming to Thailand to do a bit of travelling as well, it's nice to have the time to do so.
All in all, yes, the pay is lower than a lot of other places, but the work is dead easy, all adults, no kiddies, air-con classrooms, plenty of materials, pre-set curriculum, lots of opportunities to meet decent Thai folks, tons of vacation time if you want it -- when I return to Thailand, I'll be back on AUA's doorstep.