I don't find modes useful at all, even in doing Greogorian chant. Mostly I use this knowledge to deal with people who irritate me by dismissing any creative piece of traditional music with a shrug and "It's modal."

I think you make a mistake dismissing modes in this way, Leeneia. A great many traditional tunes are based on scales which are not the major/minor of modern western tonality. In fact one way of looking at it is that the modern major and minor scales are simply two of a number of possible modes. The different modes give a different "feel" to a tune, just as major and minor tunes are different in feel.