This bug has been reported on Ubuntu Launchpad as:
  https://bugs.launchpad.net/bugs/327535

when I logged in, apport reported this crash of xfce4-cpufreq-plugin.

ProblemType: Crash
Architecture: i386
DistroRelease: Ubuntu 9.04
ExecutablePath: /usr/lib/xfce4/panel-plugins/xfce4-cpufreq-plugin
NonfreeKernelModules: nvidia
Package: xfce4-cpufreq-plugin 0.2-2
ProcCmdline: /usr/lib/xfce4/panel-plugins/xfce4-cpufreq-plugin socket_id 10485816 name cpufreq id 12069553770 display_name CPUFreq size 26 screen_position 1
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
Signal: 11
SourcePackage: xfce4-cpufreq-plugin
StacktraceTop:
 free () from /lib/tls/i686/cmov/libc.so.6
 g_free () from /usr/lib/libglib-2.0.so.0
 ?? ()
 g_cclosure_marshal_VOID__VOID ()
 g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
Title: xfce4-cpufreq-plugin crashed with SIGSEGV in free()
Uname: Linux 2.6.28-6-generic i686
UserGroups: adm admin audio cdrom dialout dip floppy lpadmin netdev plugdev powerdev sambashare scanner video

Stacktrace available at: http://launchpadlibrarian.net/22506786/Stacktrace.txt