I heard the term "legacy media" for the first time at this conference. Why am I always the last one to hear this stuff? A quick Google search pins the term's origins at least to 1998. This 2004 discussion treats the term as relatively new... but isn't everything we're doing new?
Computer folks refer to old hardware and software as "legacy systems," the old junk that folks still patch into the network, even though the original vendors stopped supporting it (or disappeared from the market) years ago. So legacy media would be the old media, the mainstream newspapers, radio, and television that used to dominate the market and now finds itself sharing mindspace with the new journalism of the Internet.
Legacy carries the loaded suggestion that the media so tagged are dead-end enterprises, on life-support, waiting to die. The term is thus more argumentative than descriptive: calling the Sioux Falls Argus Leader "legacy media" stakes out your advocacy of the argument that the mainstream media will die, or at least mutate into something unrecognizable. Any one of us could turn out to be legacy media. Blogs, wikis... how long until the kids with the next new idea start calling us legacy media to hasten our demise?
Suppose we finally kill off big media... yikes! No more New York Times for me to quote on my blog! Where would we get all the news that we talk about?
Don't worry: someone would go get those stories and make them available. We'd go back to some 19th-century-style correspondence... and we might still find the stories that interest us just as quickly, thanks to Google and the joys of search. We all can be storytellers; we all can contribute a little bit to the collective knowledge and make that little bit available to everyone.
A related note: Remember the Cray supercomputer? Now there's a legacy system I'd like to have in the basement. And they're still in business! Anyway, Arnie mentioned that the Cray supercomputer, once the fastest computer in the world, was replaced by a thousand PCs. You don't build one massive machine; you just wire a whole bunch of regular everyday machines together and get them working together. (The majority of the 500 fastest supercomputers today are computer clusters... and over 3/4 of those 500 supercomputers run Linux... open source software.)