Mixerman and others pointed out some very interesting and useful delay applications in my thread there:

(Dead Link Removed)

I shy away from "one size fits all" approach.
Sometimes the slap wants to be 80ms, sometimes 130ms. Sometimes the delay wants to be 1/4 note, sometimes 1/2, sometimes dotted 1/16. This will depend on the arrangement, available space in the mix, style of music, how many cups of coffee I've had, particular performances of all interacting elements of the song, etc.

Walk into every mix with a clean slate and an open mind.

Sometimes I like the way a tape delay like a Space Echo can splatter the taps around a little more randomly than a digital delay.

If it's a sparse mix, the digital echo can be a little too clean.