I use an MXR Carbon Copy analog delay and I like to set my delay at around 230 milliseconds at only about 1/3 of the volume of the original note. This way it kinda sits there in the background adding texture and space without overwhelming the note. I don't really care about matching the delay tempo to that of the song - I prefer to use it as a spatial effect rather than a rhythmic one. You can hear my approach to delay in this video:
http://www.youtube.com/watch?v=iQUb3KrLQz0 - it's almost like reverb rather than delay. Listen closely to the very last chord and you'll hear how fast I've got the repeats set.