Well, clearly somewhere in the English speaking world spik3y has a vulgar meaning. That is when the "plum" replacement usually kicks in, and I've seen a lot of interesting conversations on what it will and will not allow. I've also seen it sometimes allow the original word if the original post is edited, then saved. So I suspect that it mostly looks at newly typed content. But this isn't completely true, because this isn't consistent.
Who knows what the plum the moderators had in mind for spik3y.
EDIT: Ok, this from Urban Dictionary - Sp!ky (no "e") basically someone who is frisky. But only mildly. (Maybe meaning a step down from h0rny?) Enough to make out, but not quite enough for woohoo. So I don't know how it falls into the "plum" category, since I would consider it R-rated at best and no worse than the term "woohoo." Go fig.