I think picking up a dictionary in the middle of a plot can be annoying but some words can be understood by the context only. Also I agree with @viksorion that reading is an enriching experience and learning new words is definitely one objective with which i tend to pick up new authors as each author has a way of expressing same feelings in a different way. Yes unnecessarily putting words just to prove one's scholarly mantle should be avoided but I support use of new and difficult words in a book
Too bad the author can't sit with the dictionary to explain things. You can't get things at hand, have to work a bit. And with new readers the words are right at yourfingertips. If you don't have a reader than the google is not far away.
And more often than not you can make out whether the author really has the style of writing or just showing off. The words fit in, the ideas are flowing, so you enjoy. Otherwise its a pain to read those books
Technology does make us lazy. No dictionaries, but I would love to pick the brain of a few authors whose books/characters left me utterly confused.
Like @Mousetrap said, the golden rule is that the word should be self-explanatory in reference to context. Mr T-Rex sounded arrogant with the whole an ancient creature soon to be extinct, snuffed out in a cloud of incomprehension.