FYI, Matthew Thomas mentions the rationale for this in his review of
the HIG:
http://mail.gnome.org/archives/hig/2001-October/msg00052.html

"Buttons accessed by pressing Enter or Escape should not have an
access key; this would only slow users down, by encouraging them to
look for an access key instead of using the quicker Enter or Escape
method of activating the button. Indeed, giving an access key to a
`Cancel' button would make it *less* obvious that it could be accessed
by pressing Escape, because there would no longer be anything
distinguishing it visually from an action button."

I think not putting mnenonics on OK only works if:

 - OK is always the default button (even if it is "unsafe")
 - We don't move the default to buttons with the focus
   (Something that wasn't finalized in #53709

As for Owen's first point, in those extremely rare cases where `Cancel' is 

the default button, the main action button (which is highly unlikely to be 

labelled `OK' in such cases) should indeed have an access key. Keep in 

mind that hackers consistently overestimate the probability of users making 

mistakes, so they tend to want to make `Cancel' the default button more 

often than it should be. (Or even worse, they suggest there should be *no* 

default button.)



His second point seems wrong: MS Windows moves the default button with 

the focus, but it still doesn't give access keys to either the Cancel or OK/

equivalent buttons, except in a few very badly-designed programs such as 

ICQ. (Mac OS X doesn't move the default button with the focus.)

Hmm, I usually am in the position of having other people
tell _me_:
  
 "Just because windows does it doesn't mean it's right"

I think I have to bring that this time :-)

  His second point seems wrong: MS Windows moves the default button 
  with  the focus, but it still doesn't give access keys to either 
  the Cancel or OK/equivalent buttons

That windows doesn't do it some argument that it might
not be necessary to add the mnemonics but doesn't conclusively
indicate that I am _wrong_. 

I'd think it's a fairly nice touchto have a keybinding that 
activates the OK button without regard to where the focus is;
otherwise the user has to look at where the focus is before
deciding how they are going to select the button.

We're just dicsussing this in our weekly HCI meeting at Sun, I'll let
you know what the outcome is  :)

Well, we discussed it for a while, and concluded that:

- The Java guidelines team discussed the very same issue at some
length, and eventually decided OK and Cancel should not have access
keys, but that everything else should have (including default buttons
that didn't happen to be labelled OK).  Despite a long mailing list
discussion at the time, though, the precise rationale unfortunately
remains unclear  :/

- We thought there should probably be a GNOME guideline to say that if
there's an OK button in a dialog, it should be the default anyway (or,
more accurately, the only button capable of being the default)

- All that said, we couldn't come up with any strong usability or
anecodotal evidence to suggest that having access keys on OK or Cancel
would be desperately bad, except that it would use up two more access
keys fairly unnecessarily, and it would "just look odd" to anyone
who's used to Mac, Windows, Amiga, Java etc.

Unless we decide to remove movement of the default action to
the focused button (bug 53709) I think there's a fairly convincing
argument for leaving it is.

So, putting until we have a final decision on 53709... it's easier
to remove them here later than to add them back, since adding
causes potential mnemonic conflicts, removing won't .

(Just adding comments in response to Owen's recent "should we fix 
for 2.2" email)

The current draft of the HIG says that instant apply dialogs, which 
are now the norm in GNOME, shouldn't have default buttons.  As long 
as that guideline remains I think it's probably better to keep the 
mnemonics on OK and Cancel, although I can't say I've grown to like 
them any more over time...

I'm taking that as a WONTFIX, since I don't like having a
million "need to consider this more in the future" bugs
open :-).