Of course, you'll have to get one of the new digital TVs and watch DTV programming to get this capability. There are captioning companies that edit other programs for reading speed, which has sparked many interesting debates. Many reporters and public speakers will deviate from their notes or scripts as they go, and if there isn't a realtime captioner, the captions won't match what is being said. The dialog may be changed and re-dubbed after the captioning is done. This can lead to captions for dialog that doesn't match, or even doesn't exist in the final tape.
Swear words lead to other inconsistencies.
It is the stated opinion of most, if not all, captioning firms that if it's in the audio it should be in the captions. For a lengthier discussion of this subject, see my Newswaves column from April 1998, entitled From the Mailbag. The last half of the column is a discussion of obscenities in captioning. I haven't yet had an opportunity to see this unit in action. The most common reception problem is dropping of a frame of video, which takes out the two characters contained in that frame, so missing letters usually come in pairs.