>I think the default "Meta" key on a standard PC keyboard maps to the "alt" key.

I believe you are right but, as the Alt key by default brings up the Window menu
on Windows, there seems to be some conflict there.

In my experience every keyboard I've used has had an Escape key, most of them in
the top left corner (or thereabouts) so, rather than having to determine what
the particular system I am using at the time defines as the Meta key, I tend to
stick with Escape. This is particularly useful in my experience when I am using
a PC X Server to log into Unix boxes and so on (which I do regularlY) as then I
don't have to mess around with the X Server to make it pass Alt key presses to
the application.

Just my opinion of course, but...