GroupLayout is integrated into Mustang
I'm just relaying the information from JavaLobby but GroupLayout has been integrated into Mustang b76. GroupLayout is the layout manager that makes NetBeans' Matisse GUI builder shine. So, go grab Mustang, download NetBeans 5.0 and enjoy!
Please note that this new features still required the approval from the JSR 270 EG. You can find more information about Java SE 6 JSR on the JCP web site: http://www.jcp.org/en/jsr/detail?id=270