  In this paper, we show that the complete scalar-flat Kahler metrics
constructed by Abreu and the author on strictly unbounded toric 4-dimensional
orbifolds have finite $L^2$ norm of the full Riemannian tensor. In particular,
this answers a question of Donaldon's on the corresponding Generalized Taub-NUT
metric on $R^4$. This norm is explicitly determined when the underlying toric
manifold is the minimal resolution of a cyclic singularity. In the Ricci-flat
case corresponding to gravitational instantons, this recovers a recent result
of Atiyah-Lebrun.
