It occurred to me that Lennart Augustsson wrote in gmane.os.netbsd.current:
> I'm very interested in the circumstances involved in this,
> since I've never had a mouse go dead myself.

My Microsoft optical mouse dies on a semi-frequent basis, but I suspect
that this is related to it being connected via an (electronic, PS/2) KVM 
switch. Every now and then (Once per week, or so), the mouse will
shutdown - but *only* on the NetBSD output on the KVM! Restarting X will
get it back.