[this piece will probably undergo refinements before become a real page:]
I was talking to someone today who wanted to start captioning their videos.
This seemed like a good use of a volunteer, so I gave them some starting out info.
The Two Easiest Ways to start CC online:
Both subtitling sites are able to add subtitles to common video formats, and are both able to export the caption files for import into youtube.
Neither one, however, embeds nicely into the hosted version of WordPress. (work on that, Matt?)  The dotSUB version is embeddable through VodPod video collection.
Embedded sample: http://thecaptionedinternet.blogspot.com/2011/05/grand-rapids-lip-dub-synced-with-lyrics.html
Tutorials: They have training videos that are shown as you along step by step.
Easy/Fun – once you have the words in, the timing is like playing Rock Band.
Allows importing of a written transcript -then you are just setting the timing, not typing. *
Cons: Harder to fine tune.
Vodpod videos no longer available.
Embedded Sample: http://www.captionfish.com/movies/larry-crowne
Hosts a copy of the videos (good for stability)
Adjust Accuracy within 1000ths of a second
No way to import a transcript
The DCMP article contains the best overview of online captioning, and includes captioning guidelines, good to read if you are just captioning “talking head” videos, and a more detailed Captioning Key with information on how to convey more complex information.
* Bonus Article: Importing transcripts into universal subs:
You can create a transcript with Dragon Naturally Speaking (Windows also provides free voice recognition, XP and later), by “echoing” the words that are spoken on the video into your chat headset microphone.
Then format your lines and upload it into universal subtitles.
How you format the transcript determines how they display on the screen.
1) Hit enter twice to separate each subtitle;
2) You cannot submit subtitles longer than 3 lines (2 is best).
The import method is not obvious either: Click upload subtitles, then click “Paste in Transcript”