There is a big difference in conditions between the sois (smaller roads) and the big roads (like Sukhumvit, Petchaburi, Rama IV, etc).
These days the sidewalk condition on the major roads is better than it used to be and a lot of the obstacles (like old phone booths and random utility poles) have been removed. But there are still too many cases where it's still easier to ride on the side of the road, and the busses and ignorant vehicles are a danger. This is an area where bicycle lanes would help keep cyclists safe.
On the sois, there is usually way less traffic and everything goes.