There are a few ways to use subtitles that haven't been mentioned. You can:
1)Indicate what the characters are saying in the anime.
2)Make them say whatever you want them to say.
3)You can subtitle the song or alternately put in poetry or the lyrics of a song in the instrumental version.
4)Another thing you can do with titles is to tell the story of the video by making up titles yourself. Titles seem to be most useful instrumental videos but can be used in a variety of situations.
5)Titles can be used in the beginning of a vid to match up characters in the anime to characters in the song.
6)Finally they can be used for dramatic effect.
Parodies and trailers also have their own specialized use of subtitles/titles but barring those it's generally a good Idea to replace the subtitles with your own titles.
Pie Row Maniac wrote:My friends got a girlfriend and he hates that bitch
Damn, I remember an eva vid to that song (the one with the original artwork) that I can't find anymore... Stupid Kazaa hating campus networks.

If anyone could send it to me I would op a video of theirs and worship them as God, you know, the usual.