There seems to be a new connotation being associated with "pleading the fifth". If memory serves me correctly, in the past, when individuals were pleading the fifth they usually stated something to the effect of " I refuse to testify under the grounds it might incriminate me." Whether correct or not, this statement might lead one to assume guilt on that persons part.
I don't know if I haven't noticed it before but in light of the recent Enron scandal, many of the executives who have been called to testify have also pleaded the fifth. They however, have invoked a different wording that on the surface (at least to me), sounds less incriminating and actually sounds like their invoking their rights rather than refusing to answer. It goes something like this. "I refuse to testify under the protection afforded me under the Fifth Amendment of the Constitution of the United States of America.
Subtle, but a whole new meaning. By leaving out the "incriminate me" portion, a message is sent and guilt is not implied. By using the terminology "protection afforded me" it sounds like the person is being persecuted by the authorities and the implication of guilt is somewhat transferred. Given the choice between the two statements, I certainly would choose the latter.