Also, last night I figured something out: My IRC connection hasn't been freezing, really; when I joined the same channel using both computers, I found out that my text and pings were getting out from my computer, but nothing was getting in. It's as though I'd joined IRC normally but with everybody and all messages and notices on /ignore.
Hang on, here's a late-breaking bulletin: I'm on IRC with both machines again right now, and I left it on long enough that the connection on my machine got disconnected from the server. It auto-rejoined, and now it works! That hypothetical all-encompassing /ig has disappeared!
Except I remember now that the first day I had the problem, I left my IRC connection on longer than this, and that didn't happen. So there's no guarantee it'll ever happen again.
Anybody have any clue what's going on?!?
EDIT: I tried disconnecting and rejoining, and the Evil Giant /ig came right back.
The Data Doctors guy is coming tomorrow to take a look at my computer and see if he can figure something out.