I've always found tune/melody writing the hardest part of a song, plus I have the brain of a goldfish and very little composing ability so I'm one of the tune thieves mg hates so much! :) If I can't write the note progression down immediately, I will forget it. It appears that I can only write in the minor key and I've only ever written 2 tunes that I've remembered - one I composed on my mobile phone composer (and what a pig it is that my subsquent phones don't have this ability) and one on the piano during an enforced stay in the dining room. I have since discovered that the second of my compositions is a tune I heard several times about 15 years ago and I've managed to reverse a couple of lines. What the hell, I'm keeping it as mine because it goes to a song that someone I like very much wrote.

Anyhoo... it's the marmite argument all over again. Either you think melody is important or you don't. Those with an instrumental background will tend to listen to the music first, whereas those with a lyrical grounding will pay more attention to the words. The acid test is using the same words with different tunes - Mass settings and other religious choral pieces are good examples.

A good, memorable melody is vital if you want your song/tune broadcast to the world by whichever means. If you just want a showcase, one-off performance then it's not so important. As my experience with navel-gazing dirges has been limited of late, and I can't remember the tune of a single one, I would suggest that these were 'show/off' performances that only require the one airing to 'get it off his chest' as it were.

Mozart wrote music for the Church and so his mass settings are melodic, memorable and meant to be sung as part of a religious service. The congregation would know the words and so the melody was the important feature. Many of todays religious songs concentrate on evangelising and reassuring congregations from different liturgical backgrounds, so melody is quite often secondary to the lyric.

As for what is a melody? It's whatever progression of notes you hear in whatever context that makes you want to hear it again. Just as there is rhythmn in life (and the basement and the street), there is music in the wind, lyrics in the trees and melody in water.

LTS