I only learned about this back around 1998 when I was doing Sick Puppy Comix. I got a letter from the National Library of Australia (in Canberra) letting me know that they had copies of SP #1 and 2, and if any other copies had been published to kindly send those for 'Legal Deposit'. It was news to me. Not only had I never sent them any Sick Puppys in the first place, but I didn't know what the hell 'legal deposit' meant. It was pretty cool to receive that letter though, and I had fun wondering how the National Library had gotten hold of my comix.
Anyway, I had forgotten all about this legal deposit thing years ago, but the subject came up recently when I met a friend for drinks just before Christmas. She's a Research Librarian, and somehow the conversation got around to the subject of legal deposit. I told her about that letter I received in 1998, and said something about how surprising it was to me that National and State libraries collected stuff like 'underground comix', 'Adults Only' type stuff, but my librarian friend told me I would be amazed what other stuff they collected. I said, what, they don't collect porno magazines do they? She smiled and said yep, they sure do. Underground comix and porno mags are publications, and like any other publications, have cultural, sociological, historical, etc., value. That's pretty cool, isn't it?
So that was really great to hear about, and perfect timing to be reminded about this legal deposit business! So now I'm mailing a copy of Blackguard #1 to the National Library of Australia, and a copy to the State Library of New South Wales, and I urge my fellow comix- and zine-publishing friends to do the same. I'm sure you overseas dudes have something similar where you are, but here's a link to information about it for Australians:
Legal Deposit info