I've been getting nothing when I click my "keep digging" things, sometimes. Most other blogs that I've been to that use those haven't been having the problem, though I once had it happen over at Infophilia. It's happened on my laptop and office computer, so I doubt it's computer-specific. It's also appearing on posts where I leave out the [span id="fullpost"] tag.
A bug in Firefox? An html error that shows up and fixes itself? Anyone?
Just checked the June archives and it doesn't work there, either. If there's something wrong with the html, it's not in the front page posts themselves.
UPDATE: Fixed! Thanks, Matt.