FWIW, I was taking to a Shimano rep today and asked what's the difference between Ultegra and DA. He said, DA has slightly better metal (accounts for price difference), the finish and the minute weight differences; otherwise the engineering design is the same.
I have a 27 year old bike that has DA. It still works flawlessy today. I have an 2004 bike also (all Ultegra).
Personally, I'm very pleased w/Ultegra. I can afford it but don't see the need to buy DA. I don't group ride or race so I really don't have anyone to impress w/DA, haha.
..rickko..