I've noticed a few references in recent commit logs like this: See additional discussion in Bug#9939.
My preference has been to use the slightly more verbose http://bugs.gnu.org/DDDDD, on the principle that that will be more accessible to most people. I.e., you can probably just click on it, or mouse-then-click. While for the "Bug#...." form, one would have to know the URL prefix. Preferences to the contrary?
