Found an error in Google Webmaster Tools and went to check it out. The short URL is: http://spherical.org/s/8- which 404s. The short URL target doesn't 404.
Tried: http://spherical.org/s/8%2D, figuring I cuold end-run it by editing the database, and Firefox refreshes to the former then 404s. :\
Went to the tags blog, opened the post in the editor, so I could reset the short URL, and the Yourls widget isn't there. Yourls is network activated, so it should appear. Perhaps the tags blog population of the posts table screws this up somehow.