They're basically a metal cage on three wheels with a driver sitting on a seat in front steering and contributing more smog to this already-polluted city.
Riding in one can be like a rollercoaster if the traffic is not too bad. It can be fun but dangerous/scary if you've got a loony in front driving in the wrong lane (on the wrong side of the road) just to try and beat the traffic. Yes, that did happen to us and it was not nice.
It's not just riding in them. In this city, you've also got to make a real effort not to be run over by one.
And before you've even got in, you have to bargain - like this:
Me - "To Khao San Road?"
Driver - "How much you want pay?"
M - "30 baht?"
D - "Hmm.. bad, bad 70 baht" *frowns and waves hands*
M - "40 baht?"
This goes on for a while until we agree on 50 baht and no stops.
This means he won't divert from our 15 min journey to Khao San road to drive us 30 mins in the opposite direction to take us to a top quality tailors/jewellers/tourist tat centre - just so he gets petrol coupons as commision from the shop. From the way I see it, he probably uses so much petrol taking us all that way in the wrong direction that he's definintely spent the petrol coupon before he's even got it! But anyway, it's a scam you try to avoid.
Even so, we still managed to get a bit lax on Friday and ended up visiting two jewellers, a tailors and a carpet shop...