Okay, here's a mystery.

I ssh home.  A lot.  If I leave an ssh connection idle for maybe 15 minutes,
it generally hangs.  Sometimes, if I open a new ssh connection to it, the old
one recovers.

I thought "well, of course, this is just failures in the NAT gateways I'm
behind".  (Say, in a hotel, or a coffee shop.)

But.

Last Tuesday, I was in a coffee shop with a friend.  A bit before I got there,
he ssh'd into my home machine, where he has an account.  An hour and a half
later, I noticed him logged in, and he said "oh, yeah, I'm still logged in",
and sure enough, he's still logged in, and his shell connection is fine;
meanwhile, mine are timing out.

My home box is currently behind NAT, but I had the same problem before it
was.  I don't know why this is the case.  This only seems to happen using
a NetBSD box as a client.  My friend's box is a Mac.  This has happened
over cell phone wireless (ppp0), 802.11b (wi0) and wired ethernet (fxp0).

-s