Fear not, he's just a troll...
Now while I highly doubt that they will be successful, action should still be taken against someone who makes a threat like that.
Nah, not worth the time or the effort. The moderators should just destroy the account, and forget all about it.
The user had just created an account, so removing the answer and banning the account is not necessarily enough.
You're right, that's a problem. Stack Exchange doesn't make it too hard for someone to create an account just to post crap. So far though, the benefits far outweigh the troubles, and although at times it gets a bit tedious for us moderators, let's just concentrate on the positives.
I believe further action should be taken to ban the user's IP address from ever using (and possibly even visiting) any of the Stack Exchange site's again.
IP address bans don't really work, we can never be certain where (s)he's posting from.
I am creating this because I have noticed that Stack Exchange does not have an existing policy on threats. Wikipedia has one, and I think we should too
4. Restrictions
Subscriber is responsible for all of its activity in connection with the Services and accessing the Network. Any fraudulent, abusive, or otherwise illegal activity or any use of the Services or Content in violation of this Agreement may be grounds for termination of Subscriber’s right to Services or to access the Network. Subscriber may not post or transmit, or cause to be posted or transmitted, any communication or solicitation designed or intended to obtain password, account, or private information from any Network or Service user.
(blah blah blah, more legalese)
