At one level, this concern is justified, since blog posts are transient, can be deleted, altered (including the dates) or enhanced subsequently to publication, which means that they are an unreliable witness. Of course, that's also the reason blog posts are valuable - because they're not bogged-down-in-the-morass-of-formal-publiations, but the subtlety of that point was a little beyond most (not all) of the people at Saturday's conference.
One suggestiong for a possible "solution" to this non-existent problem was WebCite:
WebCite, a member of the International Internet Preservation Consortium, is an on-demand archiving system for webreferences (cited webpages and websites, or other kinds of Internet-accessible digital objects), which can be used by authors, editors, and publishers of scholarly papers and books, to ensure that cited webmaterial will remain available to readers in the future. A WebCite®-enhanced reference is a reference which contains - in addition to the original live URL - a link to an archived copy of the material, exactly as the citing author saw it when he accessed the cited material.
Individual writers, scholars and students wishing to use WebCite for archiving and citing web references can use WebCite free of charge without having to apply for membership.
Personally, I'm not interested in trying to fossilize the Internet - I'd rather it was more dynamic. But I can see ways in which WebCite could be very useful. Although Creative Commons licences are irrevocable, that doesn't stop people trying, and I personally have had a few instances where publishers have complained to me after I used a Creative Commons-licenced image published on Flickr and the licence had subsequently been changed. For me, increasing the take up of Creative Commons-licenced resources could be the biggest payoff of WebCite.
Maybe you can think of other uses?