tones

A couple of silly questions on tones.

Does anyone know if there is an even distribution of tones amongst the characters or if someone has ever done a breakdown and given the percentages.I seem to be noticing a lot of fourth tones lately [maybe cos it's my fav though]?

I also take it there has never been any rhyme or reason to how tones were assigned [presumably because the roots are so ancient].Would have been nice n tidy if all verbs were 4th tone,nouns say first tone,grammar particles neutral,adjectives maybe third tone,question particles 2nd maybe.But keeping us guessing keeps things interesting I s'pose.