As another anecdotal data point, I had a technical discussion go awry this week because someone was pointed to my slides, which I'd written assuming the sessions would be recorded (ie, I didn't spend time on extensive speaker notes). The reader got confused without the context of the spoken talk, and wrote a moderately-hot flame about what they assumed my talk "must have been about" based on the slides (missing the point, I'm afraid).
So: without video not only are the slides I posted not useful, they seem to have been actively *detrimental* to the cause. It would be better if I hadn't posted them.
Certainly part of the blame is mine for being overly clever in my talk (jokes and tone of voice being hard to capture on slides). But I do wish we'd taken the time to archive this little bit of "the world's knowledge" when it happened. Looks like I'm going to have to re-present the talk at some point in order to get it properly recorded.