So here's a list of Weird Stuff(tm) I'm now noticing regarding network connectivity:

1. ssh and NNCP (port 5400) to a friend's box, also on Comcast, don't work.

2. traceroute to friend's box works but doesn't recognize end of route. I get additional hops of "* * *" beyond where the traceroute should end.

3. ping doesn't work to friend's box. (big surprise)

4. ssh to either my box or the same friend's box from T-Mobile's network (using JuiceSSH from my phone) doesn't work.