A derivatives tag was created on November 20, in this question; I didn't notice when I answered, or I probably would have deleted it.
Do we really need a derivatives tag? I realize we have tags for integrals and limits, but the fact that it went so long without this tag suggests it may be somewhat redundant...
Update. Okay, seems like the (limited) consensus is that, yes, we should have it.
Perhaps only in conjunction with the [calculus] tag (or the [multivariable-calculus] tag if it is a partial derivatives question, etc.), and only when the question is about computation of derivatives rather than simply questions about derivatives. I guess it would be too much to change the name to something like [derivatives-computation]...
It's unfortunate the tag excerpts seem to be read about as much as the FAQ by users; we keep getting questions tagged [algebra], even though the excerpt explicitly screams not to use it at all...