learnedax and I were just discussing things like this last night. We want Twitter posts (and I'm active twitter user) to be more in the ephemeral, and LT instead pushes them into a realm of less ephemerality. (I've had to make the context/nature of Twitter/LJ argument a half a dozen times in the past year in different journal comment threads) Ideally, Tweets would autokill after 24 hours or so, when the chance of any relevance to the reader is almost nil. It would also be cool if you could manually set an expiry date/time, so that if you're tweeting about going to the diesel later today, the post can kill itself in 6 hours, but if you're tweeting about your housewarming party next week, it can stick around until next week....

Essentially building on the existing tagging notions to bring another form of metacontext into play.