It is my belief that far too often too much prominence is given to ornamentation. It is exactly what it says and so is not essential to the tune. When I am learning a new tune I focus of rhythm and phrasing and only once I am comfortable with the tune do I attempt to add ornaments. In quicker tunes I rarely ornament as too often it slows you down and the rhythm suffers.

I remember when I was attending the Folkworks Caedmon classes at the Sage a couple of years ago, the regular flute and whistle tutor was away one week and an Irish Flute player covered the class on that day. She taught us a slip jig and someone asked about ornamentation. After commenting she did not use a lot of ornaments herself, she made some suggestions and then asked us to play the tune through to try some out. I played with almost no ornaments and then apologised that I hadn't added many ornaments as I was still not familiar with the tune. Her response was "Ah, but you were shaping the melody".

A comment on the clip of the Liverpool Hornpipe I linked to. The actual tempo that the fiddler was playing at was not particularly important, it was the accuracy with which he maintained the tempo even when playing quite slowly. The tempo is much slower than we normally hear the tune played at, but it does show that a tune normally played quite quickly can be very effective when played slowly. You have to play it well, though and that fiddler certainly did.