[edit: a how-to article will be included in the 1.7.9 release; here is a preview]
One of the more important topics scheduled for the upcoming Git 1.7.9 release is for a contributor to ask the integrator to pull a signed tag and for the integrator to merge such a signed tag to the history. This has already been used in the field by Linus but there wasn't a good automated way to view and verify the signature after such a merge is made.
I started working on a follow-up topic to teach "git log --show-signature" about these merge commits, and have a working code in today's proposed updates branch ('pu'). Hopefully we can have this feature, possibly with some clean-ups, in the same 1.7.9 release, if we get enough help from the contributors in the development community.