Funny thing is, I tried using negative keywords earlier in the same session, so it's like the Great Google fairy was watching. Or something.
This is the first time you can add negative keywords right at the beginning of the Keyword Tools process, no?
The Negative Keywords tab will come up with potential negative keywords for your campaign, which is a nice feature. However, what I really had hoped it would allow me to do is to use negative keywords right in the Keyword Variations tab, i.e., tell it I was targeting, say, [card games] and then add [-pokemon]. Alas.