Okay, I got into my box and I think I've discovered what the problem is. As I mentioned in an update to last night's entry, I couldn't get to my box from another box I have access to, so I began to suspect it was something on sshd's side. When I checked my logs, I was able to confirm the likelihood of this. Here is the relevant bit from auth.log:
Nov 24 12:57:56 nexus libsafe.so: version 1.3
Nov 24 12:57:56 nexus libsafe.so: detected an attempt to write across stack boundary.
Nov 24 12:57:56 nexus libsafe.so: terminating /usr/sbin/sshd1
Nov 24 12:57:56 nexus libsafe.so: overflow caused by memcpy()
Now this caught my attention, because for the past two days, I've been getting a handful of program crashes from 'attempt to write across stack boundary.' Most commonly, whenever I try to view an e-mail that is more than about 1k in size, it's been dying on me too.
So, I thought back to what I've upgraded on my Linux box in the past day or so, and I remember installing the new optimized libc6 (glibc2) package, libc6-i686 (I have a dual PPro box). Ever since I installed that, I've been getting that error.
So, I went ahead and removed the libc6-i686, using the default 'normal' libc6, and restarted sshd. It seems to be running fine, now. And, mutt has stopped crashing on me, too. ;-)
So, for the moment, it looks like life is good. ;-)