The headline comes from a very old Bugs Bunny cartoon (The Old Grey Hair, 1944, by Robert Clampett), in which the rabbit and hunter are transported to the far-off future, to the year 2000. (The title panel comes from Dave Mackey's site.
I mention it because the invention is just five years late, and is coming to a Web near you as an option.
XML Smell,based on the open source XML specification, will require an XML parser and a "smell pallette" which, I assume, would be a peripheral device. Once the pallette is miniaturized and mass-marketed, smells in theory could be emanating from e-mails, SMS messages and Web sites.
The trouble is, of course, that it wouldn't take very much of a hack at all to conjure up quite nasty smells, and you can't control the experience -- the people around you smell what you do.
I guess I'm like the Carl Stalling of the cartoon headline. "It'll never work."