> So in the absence of any font metrics or font identification,
> what would you suggest?

Perhaps getting away from overly long button text?! ;^)

> I tried to get away from hard-coded
> font names; I suppose that I could just use the balloon help
> font (and hope that it's small enough), or add a Preference
> that would default to that.

That would be one way. Though if I look at the row right below (using
Atlanta 11) this seems like a reasonably narrow font for the buttons as
well.

Cheers,
  - Andreas