'Walt, whom I was pleased to bump into [...], is probably right to suggest in the comments that some energy around notifications etc has moved to Twitter: "Twitter et al ... have, in a way, strengthened essay-length blogging while weakening short-form blogging (maybe)-and essays have always been harder to do than quick notes"'
That ties in to my experience to some extent. I've just published a blog post from Sun-PASIG in Malta, which ended a month ago (not really an essay, but something where it was hard to get the tone just right), and I have a bunch of other posts in the "part-written" pipeline. Tweets are a lot easier.
But that isn't quite my point here. I'm a little concerned that the new "longevity" threat may not be the encoding of our discourse in obsolete formats, and not even our entrusting it to private providers such as the blog systems (as long as it IS open access, and preferably Creative Commons). The threat may be the way new venues for discourse wax and wane with great rapidity. We can learn to deal with blogs, we can even have a debate on whether the twitterverse is worth saving (or how much of it might be). Do we need to worry about other more social media (MySpace, Facebook, Flickr and so many lesser pals; so heavily fractured)? They're not speech, they're not scholarly works, but they have some significance (particularly in documenting significant events) somewhere in between. We could learn to deal with any small set of them, but by the time we work out how they could be preserved, and how parts might be selected, that set would (as is suggested above for blogs) already be "so last year".
BTW, part of this space is being addressed by the Blue Ribbon Task Force on Sustainable Digital Preservation and Access. I'm attending one of their meetings over the next two days, on my first visit to Ann Arbor, Michigan. Among the things we're looking at are scenarios that currently include social media. I'll try and write a bit more about it, but it's not really the sort of meeting you can blog about freely...