Netbeans IDE RC2 running on Mustang aborts on Solaris 10 (regardless of processor type, x86 or sparc) if GTK is specified.
As far as I tried
  - 5.0u6 w/ GTK LAF doesn't abort.
  - 1.6.0-rc-b68 w/ GTK LAF aborts.
  - 1.6.0-rc-b68 w/ default Ocean LAF or Motif LAF doesn't abort.

Locale seems to have nothing to do with this problem. I trie C and ja_JP.UTF-8 locales, and Netbeans aborted in either case.
The same combination (Mustang-b68, GTK) was ok on Windows XP.

In my simple testing, Netbeans RC2 w/ GTK LAF booted on some old Mustang builds (e.g. b10, b50, and b52). It aborted on b53 and b54 as well as the latest build, b68.
So, this seems to be a regression which was introduced during Mustang development phase.

=======================================================================
How to reproduce:
0. Install Netbeans RC2. (http://www.netbeans.info/downloads/download.php?type=5.0rc2)

1. Run Netbeans with specifying GTK LAF. For example,
% bin/netbeans --laf com.sun.java.swing.plaf.gtk.GTKLookAndFeel --jdkhome /java/re/jdk/1.6.0/promoted/latest/binaries/solaris-i586
or
% bin/netbeans --laf com.sun.java.swing.plaf.gtk.GTKLookAndFeel (If Mustang is set as default JDK for Netbeans)

If DISPLAY environment variable isn't set or is invalid, Netbeans displays the following warning BUT boots up and works.
  Xlib: connection to ":0.0" refused by server
  Xlib: No protocol specified
If the variable is valid, Netbeans aborts on its start-up time after displaying the following error message.
-----------------------------------------------------------------------
Fontconfig error: Cannot load default config file

** (<unknown>:24908): WARNING **: No builtin or dynamically loaded modules
were found. Pango will not work correctly. This probably means
there was an error in the creation of:
  '/etc/pango/pango.modules'
You may be able to recreate this file by running pango-querymodules.

(<unknown>:24908): GLib-GObject-CRITICAL **: file gobject.c: line 1561: assertion `G_IS_OBJECT (object)' failed

** (<unknown>:24908): CRITICAL **: file pango-engine.c: line 68: assertion `PANGO_IS_FONT (font)' failed

** ERROR **: file shape.c: line 75: assertion failed: (glyphs->num_glyphs > 0)
aborting...
Abort
-----------------------------------------------------------------------

I'm not sure if Swing is the appropriate category to submit this bug, but I'd like to ask the Swing team for the initial evaluation because this problem is LAF-dependent.