For me, the nautilus crashes only happen when ubuntu one file sync is enabled.  I can enable notes, contacts, and broadcast messages with no problem

(gdb) run
Starting program: /usr/bin/nautilus 
[Thread debugging using libthread_db enabled]
[New Thread 0xb7e61b70 (LWP 9125)]
[New Thread 0xb7660b70 (LWP 9126)]
Initializing nautilus-image-converter extension
Initializing nautilus-gdu extension
[Thread 0xb7e61b70 (LWP 9125) exited]
warning: the debug information found in "/usr/lib/debug//usr/lib/libcamel-1.2.so.14.0.1" does not match "/usr/lib/libcamel-1.2.so.14" (CRC mismatch).

warning: the debug information found in "/usr/lib/debug/usr/lib/libcamel-1.2.so.14.0.1" does not match "/usr/lib/libcamel-1.2.so.14" (CRC mismatch).


(nautilus:9106): GLib-GObject-WARNING **: invalid cast from `(null)' to `SyncdaemonFolderInfo'

** (nautilus:9106): CRITICAL **: syncdaemon_folder_info_get_path: assertion `SYNCDAEMON_IS_FOLDER_INFO (finfo)' failed

** (nautilus:9106): CRITICAL **: syncdaemon_folder_info_get_volume_id: assertion `SYNCDAEMON_IS_FOLDER_INFO (finfo)' failed

** (nautilus:9106): CRITICAL **: syncdaemon_folder_info_get_subscribed: assertion `SYNCDAEMON_IS_FOLDER_INFO (finfo)' failed

Program received signal SIGSEGV, Segmentation fault.
IA__g_str_hash (v=0x0) at /build/buildd/glib2.0-2.24.1/glib/gstring.c:134
134	/build/buildd/glib2.0-2.24.1/glib/gstring.c: No such file or directory.
	in /build/buildd/glib2.0-2.24.1/glib/gstring.c
(gdb) thread apply all but

Thread 3 (Thread 0xb7660b70 (LWP 9126)):
Undefined command: "but".  Try "help".
(gdb) thread apply all bt

Thread 3 (Thread 0xb7660b70 (LWP 9126)):
#0  0x0012d416 in __kernel_vsyscall ()
#1  0x001cd342 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0x008260ce in g_cond_timed_wait_posix_impl (cond=0xfffffdfc, entered_mutex=0xb, abs_time=0xb7660288)
    at /build/buildd/glib2.0-2.24.1/gthread/gthread-posix.c:242
#3  0x00871bbc in g_async_queue_pop_intern_unlocked (queue=0x8266940, try=<value optimised out>, end_time=0xb7660288)
    at /build/buildd/glib2.0-2.24.1/glib/gasyncqueue.c:365
#4  0x008c3d53 in g_thread_pool_wait_for_new_task (data=0x8266908) at /build/buildd/glib2.0-2.24.1/glib/gthreadpool.c:270
#5  g_thread_pool_thread_proxy (data=0x8266908) at /build/buildd/glib2.0-2.24.1/glib/gthreadpool.c:304
#6  0x008c1def in g_thread_create_proxy (data=0x826cae0) at /build/buildd/glib2.0-2.24.1/glib/gthread.c:1893
#7  0x001c896e in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#8  0x00d9ea4e in clone () from /lib/tls/i686/cmov/libc.so.6

Thread 1 (Thread 0xb7fce760 (LWP 9106)):
#0  IA__g_str_hash (v=0x0) at /build/buildd/glib2.0-2.24.1/glib/gstring.c:134
#1  0x008884f8 in g_hash_table_lookup_node (hash_table=0x826d380, key=0x0) at /build/buildd/glib2.0-2.24.1/glib/ghash.c:309
#2  IA__g_hash_table_lookup (hash_table=0x826d380, key=0x0) at /build/buildd/glib2.0-2.24.1/glib/ghash.c:898
#3  0x017f436a in ubuntuone_nautilus_udf_created (daemon=0x826de80, success=1, folder_info=0x82e2650, user_data=0x820be30) at ubuntuone-nautilus.c:1141
#4  0x017f4816 in ubuntuone_nautilus_daemon_ready (daemon=0x826de80, user_data=0x820be30) at ubuntuone-nautilus.c:1041
#5  0x007f8dcc in IA__g_cclosure_marshal_VOID__VOID (closure=0x8238c00, return_value=0x0, n_param_values=1, param_values=0x82d6638, 
    invocation_hint=0xbfffede0, marshal_data=0x17f4640) at /build/buildd/glib2.0-2.24.1/gobject/gmarshal.c:77
#6  0x007eb252 in IA__g_closure_invoke (closure=0x8238c00, return_value=0x0, n_param_values=1, param_values=0x82d6638, invocation_hint=0xbfffede0)
    at /build/buildd/glib2.0-2.24.1/gobject/gclosure.c:767
#7  0x007ff99d in signal_emit_unlocked_R (node=<value optimised out>, detail=<value optimised out>, instance=0x826de80, emission_return=0x0, 
    instance_and_params=0x82d6638) at /build/buildd/glib2.0-2.24.1/gobject/gsignal.c:3248
#8  0x00800db4 in IA__g_signal_emit_valist (instance=0x826de80, signal_id=175, detail=0, var_args=0xbfffef9c "\345m\211")
    at /build/buildd/glib2.0-2.24.1/gobject/gsignal.c:2981
#9  0x00801256 in IA__g_signal_emit (instance=0x826de80, signal_id=175, detail=0) at /build/buildd/glib2.0-2.24.1/gobject/gsignal.c:3038
#10 0x01913340 in ready_signal_idle_cb (user_data=0x826de80) at syncdaemon-daemon.c:319
#11 0x00895661 in g_idle_dispatch (source=0x82937b8, callback=0, user_data=0x826de80) at /build/buildd/glib2.0-2.24.1/glib/gmain.c:4065
#12 0x008975e5 in g_main_dispatch (context=0x8213a28) at /build/buildd/glib2.0-2.24.1/glib/gmain.c:1960
#13 IA__g_main_context_dispatch (context=0x8213a28) at /build/buildd/glib2.0-2.24.1/glib/gmain.c:2513
#14 0x0089b2d8 in g_main_context_iterate (context=0x8213a28, block=<value optimised out>, dispatch=1, self=0x81e5008)
    at /build/buildd/glib2.0-2.24.1/glib/gmain.c:2591
#15 0x0089b817 in IA__g_main_loop_run (loop=0x8273710) at /build/buildd/glib2.0-2.24.1/glib/gmain.c:2799
#16 0x0031b3c9 in IA__gtk_main () at /build/buildd/gtk+2.0-2.20.1/gtk/gtkmain.c:1219
#17 0x08080e08 in main (argc=1, argv=0xbffff424) at nautilus-main.c:583
(gdb)