I've invested years of my life in Swing development, so its a little scary to even pose the question, "Is Swing Dead?" Bank of America, our largest customer, used to do a significant amount of Swing development. These days all new projects are using WinForms, WPF, or Flex. All of these technologies are very good, and have big marketing bucks behind them (Microsoft and Adobe respectively.) With Sun gasping for air and IBM backing a competing toolkit, what will happen to Swing?
Swing benefits from elegant design, incredible flexibility and maturity, but is this enough? In addition to the lack of strong marketing support, the tools available for WYSIWYG Swing authoring lag behind Microsofts. The Java world doesn't really have an answer to Expression + VisualStudio 8. Netbeans, Eclipse and IDEA all have visual designers but they are not nearly as powerful or easy to use.
Finally, after a long period of leading the pack in terms of UI technology, Swing has now fallen behind Microsoft in keys areas. One such area is resolution independence, which WPF supports through-and-through. Another is robust data binding.
Don't get me wrong - I hope Swing has a long and glorious future. That being said, I am hedging my bets by keeping up on competing technology.