Just a quick thought in passing, I have always considered Mandarin to have five basic tones, not the often quoted four. I guess it comes down to how linguists define tones but four tones + the neutral tone in my mind adds up to five. Not using the neutral tone correctly can make works sound wrong or even change the implied meaning. I appreciate that the neutral tone has more of a role to play in multi-syllable words etc. but come on, surely it is a tone? It adds a similar mental load.
I will admit that Thai "feels" a little more like a five tone language, as the middle flat tone in Thai gets a bit more emphasis and can apply to single syllables in their own right rather than just their position in a certain word or phrase, For me though Mandarin has five tones.
Disclaimer: I am ignoring all the bits and pieces that may happen in speech like third tones that may become second (but not quite second) etc. and any extra tones that may sneak into "near Mandarin" dialects.
Anybody else back five tones???