QFT!
with the exception of invitations/event notifications, I can't think of anything else that people routinely archive or cross-post to their personal LJs. Myspace blogs, forum posts, e-mails, IM logs, text messages, whatever happens on Facebook - even community posts cross-posted to personal LJs seem the exception rather than the rule (unless the cross-poster is soliciting feedback from their LJ-Friends as well as the community/ies). Occasionally someone posts a comment they want to preserve in a kind of self-MetaQuoting way, but these daily exports seem to be unique to Twitter.
This person has a well-thought out post asking the deep questions about why people think their Tweets are more relevant to me than their IRC posts (hint: they're probably less relevant because they're far less coherent). If you use LoudTwitter, please take me off the filter you have set up for it. And if LoudTwitter doesn't allow for LJ-filters, yell and scream at them until they do.
This person has a well-thought out post asking the deep questions about why people think their Tweets are more relevant to me than their IRC posts (hint: they're probably less relevant because they're far less coherent). If you use LoudTwitter, please take me off the filter you have set up for it. And if LoudTwitter doesn't allow for LJ-filters, yell and scream at them until they do.