The Atlantic Monthly's March 2006 issue (I apologize if it's old news for you; I just now came across my clipping from it) reports:
Researchers asked seventy-one Stanford undergraduates to evaluate various writing samples; the lexicon in the samples was systematically varied, with each judge getting either a "moderately complex" or a "highly complex" version of each sample. (The researchers created the highly complex versions by replacing every noun, verb, and adjective with the longest possible synonym.)
The effect on readers of the highly complex samples? "As complexity increased, the judges' estimation of the author's intelligence declined" (50).
This finding just reinforces that great line from Lee Woods: "Bad writing makes smart people look dumb."