Somehow in the last update (as of ~08:30 BST) my gnome terminal re-acquired the "Enable Menu Access Keys (Such as Alt+F to open the File menu)" option. I had to hunt around for a while to figure out how to shut it off again. This is a nasty surprise, as well as a terrible default: terminals are meant to send your keystrokes to remote applications, and gobbling them up locally is unhelpful.
For example, Alt+F is actually "move forward by word" in any terminal application using GNU Readline, as well as in Emacs and possibly nano. It is expected by users that alt+key combinations will be sent to the terminal-using application in some form.
As an aside, this kind of bug is why I gave up on using Emacs nearly 20 years ago: one of the terminals I had access to ate ^S locally for terminal flow control, so the command combination to save a buffer locked up my session and lost my work. I lost three important edit sessions before giving in and permanently switching to vi. This kind of behavior can be disastrous for people!
ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: gnome-terminal 3.0.1-0ubuntu3
ProcVersionSignature: Ubuntu 3.0.0-12.19-generic 3.0.4
Uname: Linux 3.0.0-12-generic x86_64
ApportVersion: 1.23-0ubuntu2
Architecture: amd64
Date: Wed Oct 5 08:53:09 2011
EcryptfsInUse: Yes
ProcEnviron:
LC_COLLATE=C
PATH=(custom, user)
LANG=en_US.UTF-8
SHELL=/bin/bash
SourcePackage: gnome-terminal
UpgradeStatus: Upgraded to oneiric on 2011-10-04 (0 days ago)
Status changed to 'Confirmed' because the bug affects multiple users.