Chris Blizzard kindly drew my attention to an update on the improvements being made on the Theora encoder. Though the details given about the advances made are very technical, the end result is visible in the examples shown on the update page.

Blizzard nicely sums up the essence of these updates: Overall, regardless of bitrate, the Theora encoder is showing significant improvement, and is even creating higher quality streams than those encoded with H.264 at numerous bitrates. It's also become evident that at least some of the previous testing that showed Theora lacking were performed with utilities that didn't necessarily mesh well with Theora in the first place (ffmpeg2theora, when linked with a recent version offfmpeg, did not produce the same issues).