I hardly ever use a thesaurus. If I do use one, it's always in conjunction with a dictionary. Sometimes it's nearly impossible to find the right word on your own. Thesauruses are useful, but they need to be used with caution. Even with experienced writers.
A thesaurus is a reference, not a tool the same way a spatula or a pen is. A cook could very well blame a cook book for a bad recipe if it was printed incorrectly or just wrong.
If your vocabulary is weak, a thesaurus won't strengthen it. If yout vocabulary is strong, you'll rarely have reason to consult a thesaurus.
People with good vocabularies automatically know every word there is and don't need reference books EVER.
I bow down to you, cogito. When I have a mental blank and consult a thesaurus for words I already know but which didn't come to me at my moment of need, it's so obviously a sign of a weak vocabulary. And when I consult a thesaurus and find a splendid word I'd never heard before, applying myself thereafter to learning its every nuance and so strengthening my vocabulary ever more, I am but a lowly dependant of the Weakling's Guide to English. You're so right, you should be the judge of how often others use a tool and what they should derive from it. Everyone here pretty much agrees that the thesaurus can be used to butcher one's writing, but that its proper use has no benefits to us writers who possess vocabularies so strong is it virtually impossible to improve upon them? Well, you learn something every day.
Just to clarify, I wasn't implying that thesaurus use is inherently wrong. It is a very useful tool. I just try not to use it too often for my own writing. I don't condemn those that use a thesaurus. Some of the greatest writers use thesauruses. As with any tool, there are improper uses of it. It's a shame that so many people hate the thesaurus because of a few improper uses. I hope I put my point across in a clear manner. Sometimes I can be less eloquent than a Neanderthal.