Eu tenho o mesmo problema acontecendo. Parece que o Unity 3D não está funcionando corretamente. Não consegui descobrir qual é o problema nem como corrigi-lo. Existem muitos posts sobre o assunto.
A boa notícia é que tenho uma solução, usando o Unity 2D. Na tela de login, clique com o botão direito do mouse no item do círculo do Ubuntu à direita do seu nome, clique em Ubuntu 2D e faça login normalmente.
Aqui está o que eu recebo quando executo unity --reset
mmorris@ion:~$ unity --reset
WARNING: no current gconf profile set, assuming unity
WARNING: Unity currently default profile, so switching to metacity while resetting the values
Checking if settings need to be migrated ...no
Checking if internal files need to be migrated ...yes
[LOG]: Moving Internal Files
[LOG]: Copying subdirectory from /home/mmorris/.compiz/session to /home/mmorris/.compiz-1/session
[LOG]: Copied file /home/mmorris/.compiz/session/1099d83abd38142b6b135126642044748200000020980043 to /home/mmorris/.compiz-1/session/1099d83abd38142b6b135126642044748200000020980043
[LOG]: Successfully moved internal files
Backend : gconf
Integration : true
Profile : unity
Adding plugins
Initializing core options...done
compiz (core) - Warn: failed to receive ConfigureNotify event on 0x2000004
compiz (core) - Warn: failed to receive ConfigureNotify event on 0x1200002
compiz (core) - Warn: failed to receive ConfigureNotify event on 0x1400002
compiz (core) - Warn: failed to receive ConfigureNotify event on 0x30000b8
Initializing composite options...done
nvfx_screen_get_param:95 - Warning: unknown PIPE_CAP 30
nvfx_screen_get_param:95 - Warning: unknown PIPE_CAP 30
nvfx_screen_get_param:95 - Warning: unknown PIPE_CAP 55
nvfx_screen_get_param:95 - Warning: unknown PIPE_CAP 56
nvfx_screen_get_param:95 - Warning: unknown PIPE_CAP 59
nvfx_screen_get_param:95 - Warning: unknown PIPE_CAP 58
nvfx_screen_get_param:95 - Warning: unknown PIPE_CAP 30
Initializing opengl options...done
Initializing decor options...done
Initializing vpswitch options...done
Initializing snap options...done
Initializing mousepoll options...done
Initializing resize options...done
Initializing place options...done
Initializing move options...done
Initializing wall options...done
Initializing grid options...done
Initializing session options...done
Initializing gnomecompat options...done
Initializing animation options...done
Initializing fade options...done
Initializing unitymtgrabhandles options...done
Initializing workarounds options...done
Initializing scale options...done
compiz (expo) - Warn: failed to bind image to texture
Initializing expo options...done
Initializing ezoom options...done
(compiz:2077): GConf-CRITICAL **: gconf_client_add_dir: assertion 'gconf_valid_key (dirname, NULL)' failed
** (process:2161): WARNING **: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._g_2dfile_2derror_2dquark.Code4: Failed to create file '/home/mmorris/.config/dconf/user.CAEZMW': No such file or directory
** (process:2166): WARNING **: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._g_2dfile_2derror_2dquark.Code4: Failed to create file '/home/mmorris/.config/dconf/user.VPOGMW': No such file or directory
** (process:2169): WARNING **: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._g_2dfile_2derror_2dquark.Code4: Failed to create file '/home/mmorris/.config/dconf/user.B6WGMW': No such file or directory
WARN 2012-10-26 10:51:51 unity.favorites FavoriteStoreGSettings.cpp:139 Unable to load GDesktopAppInfo for 'ubiquity-gtkui.desktop'
Initializing unityshell options...done
compiz (core) - Warn: unhandled ConfigureNotify on 0xc00090!
compiz (core) - Warn: this should never happen. you should probably file a bug about this.
compiz (core) - Warn: unhandled ConfigureNotify on 0xc00093!
compiz (core) - Warn: this should never happen. you should probably file a bug about this.
compiz (core) - Warn: unhandled ConfigureNotify on 0xc00096!
compiz (core) - Warn: this should never happen. you should probably file a bug about this.
compiz (core) - Warn: unhandled ConfigureNotify on 0xc00099!
compiz (core) - Warn: this should never happen. you should probably file a bug about this.
WARN 2012-10-26 10:51:53 unity.libindicator <unknown>:0 Desktop file '/usr/share/applications/libreoffice-writer.desktop' is using a deprecated format for its actions that will be dropped soon.
WARN 2012-10-26 10:51:53 unity.libindicator <unknown>:0 Desktop file '/usr/share/applications/libreoffice-calc.desktop' is using a deprecated format for its actions that will be dropped soon.
WARN 2012-10-26 10:51:53 unity.libindicator <unknown>:0 Desktop file '/usr/share/applications/libreoffice-impress.desktop' is using a deprecated format for its actions that will be dropped soon.
Initializing annotate options...done
Initializing blur options...done
Initializing clone options...done
Initializing colorfilter options...done
Initializing commands options...done
Initializing cube options...done
Initializing imgjpeg options...done
Initializing kdecompat options...done
Initializing mag options...done
Initializing neg options...done
Initializing obs options...done
Initializing opacify options...done
Initializing put options...done
Initializing resizeinfo options...done
Initializing ring options...done
Initializing rotate options...done
Initializing scaleaddon options...done
Initializing screenshot options...done
Initializing shift options...done
Initializing staticswitcher options...done
Initializing switcher options...done
Initializing thumbnail options...done
Initializing water options...done
Initializing winrules options...done
Initializing wobbly options...done
ERROR 2012-10-26 10:51:55 unity.glib-gobject <unknown>:0 g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Setting Update "main_menu_key"
Setting Update "run_key"
Starting gtk-window-decorator
compiz (decor) - Warn: No default decoration found, placement will not be correct
compiz (decor) - Warn: No default decoration found, placement will not be correct
compiz (decor) - Warn: No default decoration found, placement will not be correct
compiz (decor) - Warn: No default decoration found, placement will not be correct
WARN 2012-10-26 10:52:43 unity <unknown>:0 Unable to fetch children: No such interface 'org.ayatana.bamf.view' on object at path /org/ayatana/bamf/application283295483
ERROR 2012-10-26 10:52:45 unity.glib-gobject <unknown>:0 g_object_set_qdata: assertion 'G_IS_OBJECT (object)' failed
WARN 2012-10-26 10:53:09 unity <unknown>:0 Unable to fetch children: No such interface 'org.ayatana.bamf.view' on object at path /org/ayatana/bamf/application283295483
ERROR 2012-10-26 10:53:11 unity.glib-gobject <unknown>:0 g_object_set_qdata: assertion 'G_IS_OBJECT (object)' failed