One of the grand challenges on the Web is canonical identification. Its easy enough launch resources into the aethers. If the organization is naturally oriented towards persistence, even that, in general, is tractable. One's constituents tend to howl when you don't keep this promise.
But choosing a good identifier and making it stick is pretty hard. Identifier functional characteristics often conflict with one another, and the identifiers favored by business purposes (which pretty much always carry the day) aren't necessarily optimal from a perspective of long term persistence and management.
One aspect of the problem just got easier. Google, Yahoo, and Microsoft have agreed on a convention for identifying the canonical identifier for a given resource that may be rendered under different transactional URLs.
It is a simple, elegant solution that requires no new tags... rather, a new attribute on the link tag that has been around since the beginning. No new technology: just add consensus. Search engine optimization (SEO) just got easier.
This is a step forward in making the Web a more coherent place. See, among others, Mark8t.com blog
The Buddy System: our dishwasher has a pre-wash setting with marginal carbon footprint of zero. Other sorts of footprints can be problematic.