Do you want to know when Java SE 6 will be declared final? Ray Gan offers a Mustang roadmap on his blog. Mustang slipped to autumn but the good news is it will leave us more time to fix bugs. We might even be able to merge GroupLayout (used by Matisse) in the JDK, who knows :) Anyway, do not forget you can still submit your own bug fixes.
Current Mustang builds are very stable and I use them every day to run large apps such as NetBeans, IntelliJ IDEA and Eclipse as well as many other Swing applications, like BlogBridge. I actually use the nightly builds. If you missed Tiger, be sure to be ready when Mustang comes out. With the weekly builds you should have plenty of time to ensure your products run fine on Java SE 6.