actually i've taken the bus from bangkok to chiang mai (though it was a while ago). It just worked out that the timing was ideal. I was short on time, was on koh san road, and could easily get an overnight bus that allowed me to do things in the morning. i did end up flying back but had gone on to mae hong song

As i said it was a long time ago. phuket is if i remember a lot farther away, and I'd much rather be spending time on the beach than sitting in a bus. But you're right, the bus is an experience.