Here's where I said it in 1989:
Note also how Mike himself referred to it in 1995: http://w2.eff.org/Net_culture/Folklore/Humor/godwins.law
One of these days Mike Godwin is going to say something original or funny and I plan to take credit for is as "Sexton's Law". Until then I use the term "godwin" instead of the word "steal". Feel free to godwin this meme from me.
Ironically, the reason Google groups HAS those Usenet archives is because of Godwin's law. In the early 90s Mike and I were both on Rissa's ENIAC mailing list, and whenever Mike mentioned Godwin's law I'd point out to him I'd said it first. He told me "you'll never prove it". Oh rly?
I think it was Henry Edward Hardy or somebody else writing an academic paper about Usenet that had mentioned magi@uwo to me; magi had obtained Henry Spencer's 9 track tapes - backups of ALL of Usenet. Henry had been saving them because he had a buddy that wanted all of rec.birds and it was more work to pull rec.birds out of the usenet stream and tape was cheap, so fuckit, he just stored ALL of Usenet. Magi and Co had to convert this crap to DAT, and they'd get like a foot of tape read and the heads would clog, out would come the q tips and isoproponal, clean clean clean run more tape, repaet. This took them all summer and there were parts they couldn't read, but they got all of it.
I'd talked to magi and asked him to let me know when he was done and indeed he told me and I was, I think offered copies, but more useful would be if this stuff was online; I asked Brian Reid where we could store these and he said find out how big they are. Turns out they were three terabytes, and this was 95 or so; I think my laptop had a 20 megabyte drive.
Brian suggested I talk to Brewster Kahle at archive.org and lo verily it came to pass that magi ftp'd them to archive.org or sent them tapes or something, but I did eventually verify they were online at archive.org. There were six files, half a terabyte each. Fucking great. What can anybody do with these? Google didn't exist yet keep in mind, and I think this was right before Alta Vista came up.
I'd met somebody somehow that worked for Deja News and I kept bugging them to go get the old archives and put them online. And they did! Eventually. Then Deja News was bought by Google who changed it to "google groups".
But, that's the how and why of how Google came to have all of Usenet online. Nobody besides Henry had kept complete archives; it's been well known since the 1980s the NSA had been taking a weekly feed from uunet (rick Adams confirmed this in a public post), but they claim they've deleted them all. So Henry's were the only copy.