I have the same problem, too. fglrx crashes occasionally at shutdown. I written down the whole crash dump from my screen:

 * Asking all remaining processes to terminate...       pgrades: modem-manager[915]: <info>  Caught signal 15, shutting down...
[  128.680139] BUG: unable to handle kernel paging request at ffffc900110f1000
[  128.690008] IP: [<ffffffffa0131ae4>] firegl_sig_notifier+0x4/0x40 [fglrx]
[  128.690008] PGD 12f81067 PUD 13f819067 PMD 1338c4067 PTE 0
[  128.690008] Oops: 0000 [#1] SMP
[  128.690008] last sysfs file: /sys/devices/virtual/sound/timer/uevent
[  128.690008] CPU 0
[  128.690008] Modules linked in: binfmt_misc parport_pc ppdev joydev snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwde
p r8192ce_pci snd_pcm arc4 snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq rtl8192ce rtlwifi snd_timer snd_seq_device fglrx(
P) mac80211 snd edac_core cfg80211 soundcore edac_mce_amd sp5100_tco psmouse serio_raw k10temp sparse_keymap i2c_piix4 snd_page_
alloc shpchp lp parport uvesafb ahci video r8169 libahci
[  128.690008]
[  128.690008] Pid: 1859, comm: dbus-launch Tainted: P            2.6.38-9-generic #43-Ubuntu TOSHIBA Satellite C660D/PWWAE
[  128.690008] RIP: 0010:[<ffffffffa0131ae4>] [<ffffffffa0131ae4>] firegl_sig_notifier+0x4/0x40 [fglrx]
[  128.690008] RSP: 0018:ffff8801126f3d50 EFLAGS: 00010087
[  128.690008] RAX: ffff88011d3d96e0 RBX: ffff8801329119b0 RCX: ffffc900110f1000
[  128.690008] RDX: ffff8801126f3e68 RSI; 00000000003c0000 RDI: ffff88012729c500
[  128.690008] RBP: ffff8801126f3d58 R08: 0000000000000000 R09: 0000000000000000
[  128.690008] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000013
[  128.690008] R13: ffff88011d3d96e0 R14: ffff88011d3d9c30 R15: 00007fffd652ad10
[  128.690008] FS:  00007ff489ef2720(0000) GS: ffff8800af800000(0000) knlGS: 0000000000000000
[  128.690008] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000008005003b
[  128.690008] CR2: ffffc900110f1000 CR3: 00000001126a0000 CR4: 00000000000006f0
[  128.690008] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  128.690008] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR2: 0000000000000400
[  128.690008] Process dbus-launch (pid: 1859, threadinfo ffff8801126f2000, task ffff88011d3d96e0)
[  128.690008] Stack:
[  128.690008]  ffffffffa012125e ffff8801126f3d88 ffffffff81078789 ffff8801126f3d98
[  128.690008]  ffff8801126f3e68 0000000000000000 ffff8801126f3e68 ffff8801126f3dc8
[  128.690008]  ffffffff81078a4e ffff8801126f3eb8 ffff88011d3d9c30 ffff8801126f3e68
[  128.690008] Call Trace:
[  128.690008]  [<ffffffffa012125e>] ? KCL_SIGNAL_Notifier+0xe/0x10 [fglrx]
[  128.690008]  [<ffffffff81078789>] __dequeue_signal+0x139/0x210
[  128.690008]  [<ffffffff81078a4e>] dequeue_signal+0x139/0x210
[  128.690008]  [<ffffffff8107aa9c>] get_signal_to_deliver+0x18c/0x410
[  128.690008]  [<ffffffff8100b936>] do_signal+0x56/0x180
[  128.690008]  [<ffffffff8108bb16>] ? update_rmtp.clone.22+0x66/0x80
[  128.690008]  [<ffffffff8108cd27>] ? hrtimer_nanosleep+0xe7/0x190
[  128.690008]  [<ffffffff8108b980>] ? hrtimer_wakeup+0x0/0x30
[  128.690008]  [<ffffffff8100bae5>] do_notify_resume+0x65/0x80
[  128.690008]  [<ffffffff8100c2d0>] int_signal+0x12/0x17
[  128.690008] Code: c7 00 cb 21 a0 48 c7 c6 79 4b 21 a0 8b 4c 24 08 89 c2 31 c0 e8 9e 41 ff ff eb 96 66 66 66 90 66 66 66 90 66
 66 66 90 48 8b 4f 08 <8b> 11 85 d2 78 06 b8 01 00 00 00 c3 8b 11 81 e2 ff ff ff ff 3b
[  128.690008] RIP  [<ffffffffa0131ae4>] firegl_sig_notifier+0x4/0x40 [fglrx]
[  128.690008]  RSP <ffff8801126f3d50>
[  128.690008] CR2: ffffc900110f1000
[  128.690008] ---[ end trace b5a9c7f6a2dd3242 ]---

I have a Mobility Radeon HD 4250.