Unnecessarily detailed nitpick: Data uses contractions throughout the dialogue of TNG -- there is just one episode ("Datalore" it might have been?) where they decide to make it a plot point that he doesn't use them as a way of having the rest of the bridge crew figure out that he's been replaced by his evil twin who can use contractions.

I'm pretty sure the plot point (and the ban on Data using contractions) doesn't even get a mention again in the rest of the series.