Opt/Fn as meta? (emacs on macs)

[Sunder]

Joe Davison <halting@attbi.com> wrote:
> Luckily, on both the carbon and x11 versions of emacs I use on my mac,
> one can arrange it so either Cmd or Opt is Meta..

The Esc key is so small and so far on my powerbook that I am ready to
try a different meta key. I want to understand how to do it, and if it
can lead to any problems (I will be using Aqua as well as X11
programs).

I think I'll leave Cmd alone as I see it being used elsewhere in the
system a lot. OTOH I don't encounter any use for Opt or Fn. Questions:
 
1. Is there any downside to binding Opt or Fn as meta?. Both keys are
placed equally conveniently for me, so I could just pick the less
problematic one.

2. What would I put in my .emacs to make such a binding?

S.