While personally I'm quick to recognize the attempted humor and shake off almost all alleged threats, I'd like to point out that threats far vaguer than this resulted in the permanent block of another user recently that was also thoroughly discussed on this mailing list.
Call me a killjoy if you must, but this is simply inappropriate.
I agree with you, Michael. Death threats, even when they are meant as jokes, are in poor taste and not appropriate for Wikipedia. I'm not saying the person making the above comment should be banned, of course. (In fact I suspect that Michael and I would be among the first people to protest such an idea.) But it's probably a good idea to take care that jokes can not be misread. The person making completely inappropriate comments on Jimbo's family may well have considered himself to be "making a joke" (I don't know enough of the specifics of that case to be sure).
Here's another example that I came across recently. The following is a post containing a short list of people the poster considers to be acting in bad faith and to have a revolting agenda (i.e. trolling?):
http://en.wikipedia.org/w/index.php?title=Wikipedia_talk:Blocking_policy&...
And here is a message by the same poster, made the same morning, expressing the idea that an [[AK-74]] assault rifle with the safety off is a useful tool to deal with trolls:
http://en.wikipedia.org/w/index.php?title=User_talk:SlimVirgin&diff=2194...
If one were so inclined one could take those posts together (or the second one alone) to constitute a death threat. I am not so inclined. Like Michael I attempt to be "quick to recognize the attempted humor". The AK-74 post is no doubt meant as an innocent way to compliment Sarah for her valor in resisting vandals and trolls. I would, however, have preferred another metaphor.
Regards, Haukur