When #GeoCities announced they were closing, I reset my password so I could delete my long-abandoned site before it got archived.
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In general, I think #socnet posts should be ephemeral. I’d even prefer that most posts auto-delete after a certain time period. Yes, there are always people who may save the content (so relying on deletion for after-the-fact privacy is not a good idea, and you should still be watching what you reveal in your postings), but expiration and deletion should be the general rule.
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Would you really want someone to dig up something you posted in an AOL chatroom in 1997? You aren’t even the same person as you were then.
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Archiving without specific opt-in permission? No, no, a thousand times no.