I've installed feisty, all was good untile kernel version 2.6.20-13, after that there's an acpi module freeze when i try to launch /etc/init.d/acpid:
[ 260.056000] input: Power Button (FF) as /class/input/input4
[ 260.140000] ACPI: Power Button (FF) [PWRF]
[ 260.232000] input: Lid Switch as /class/input/input5
[ 260.232000] ACPI: Lid Switch [LID]
[ 260.268000] input: Sleep Button (CM) as /class/input/input6
[ 260.268000] ACPI: Sleep Button (CM) [SLPB]
[ 260.472000] Using specific hotkey driver
[ 260.620000] No dock devices found.
[ 260.720000] BUG: at lib/kref.c:32 kref_get()
[ 260.720000] [<c01ee21d>] kref_get+0x3d/0x40
[ 260.720000] [<c01ed50f>] kobject_get+0xf/0x20
[ 260.720000] [<c025515e>] get_device+0xe/0x20
[ 260.720000] [<c0255768>] device_add+0x78/0x530
[ 260.720000] [<c01ed50f>] kobject_get+0xf/0x20
[ 260.720000] [<c01ed92b>] kobject_init+0x2b/0x40
[ 260.720000] [<eedee60b>] i2c_add_adapter+0x12b/0x280 [i2c_core]
[ 260.720000] [<eede5573>] acpi_ec_hc_add+0x122/0x16b [i2c_ec]
[ 260.720000] [<c02ecd1a>] cond_resched+0x2a/0x40
[ 260.720000] [<c0228a3d>] acpi_bus_driver_init+0x28/0x4b
[ 260.720000] [<c0229ad8>] acpi_bus_register_driver+0x82/0xb7
[ 260.720000] [<eec7e00a>] acpi_ec_hc_init+0xa/0x11 [i2c_ec]
[ 260.720000] [<c014416d>] sys_init_module+0x15d/0x1ba0
[ 260.720000] [<c0107a5d>] sys_mmap2+0xcd/0xd0
[ 260.720000] [<c01031f0>] sysenter_past_esp+0x69/0xa9
[ 260.720000] =======================
[ 260.720000] BUG: unable to handle kernel NULL pointer dereference at virtual address 0000000c
[ 260.720000] printing eip:
[ 260.720000] c01b7f4d
[ 260.720000] *pde = 00000000
[ 260.720000] Oops: 0000 [#1]
[ 260.720000] SMP
[ 260.720000] Modules linked in: i2c_ec i2c_core dock button battery container ac af_packet binfmt_misc rfcomm l2cap bluetooth i915 drm re
iserfs dm_crypt dm_mod fuse cpufreq_ondemand p4_clockmod speedstep_lib freq_table usbhid hid gspca videodev v4l2_common v4l1_compat ohci_hc
d pcmcia snd_intel8x0 snd_ac97_codec ac97_bus snd_pcm snd_seq_dummy snd_seq_oss snd_seq_midi snd_rawmidi snd_seq_midi_event yenta_socket rs
rc_nonstatic pcmcia_core snd_seq snd_timer snd_seq_device iTCO_wdt snd soundcore snd_page_alloc iTCO_vendor_support intel_agp psmouse agpga
rt shpchp pci_hotplug tsdev evdev ext3 jbd mbcache sg sr_mod cdrom sd_mod usb_storage libusual ata_piix ata_generic libata scsi_mod b44 mii
generic ehci_hcd uhci_hcd usbcore thermal processor fan fbcon tileblit font bitblit softcursor vesafb capability commoncap
[ 260.720000] CPU: 0
[ 260.720000] EIP: 0060:[<c01b7f4d>] Not tainted VLI
[ 260.720000] EFLAGS: 00210292 (2.6.20-13-generic #2)
[ 260.720000] EIP is at create_dir+0x1d/0x1e0
[ 260.720000] eax: dd2becc0 ebx: dd2becc4 ecx: dd2becc4 edx: 00000000
[ 260.720000] esi: dd2becc0 edi: dd2becc4 ebp: 00000000 esp: e007fdc8
[ 260.720000] ds: 007b es: 007b ss: 0068
[ 260.720000] Process modprobe (pid: 5292, ti=e007e000 task=eaa74a90 task.ti=e007e000)
[ 260.720000] Stack: c0126b6b 00000014 00000000 dd2becc0 dd2becc4 dd2bed06 00000000 c01b884c
[ 260.720000] e007fdec 00000000 dd2becc0 c01ed7ba dd2becc0 c01edac7 e007fe2c 00000020
[ 260.720000] ecfbd2c0 dd2bec48 dd2bed00 dd2bed06 ecfbd248 c02557a7 dd2becc0 c0362eee
[ 260.720000] Call Trace:
[ 260.720000] [<c0126b6b>] printk+0x1b/0x20
[ 260.720000] [<c01b884c>] sysfs_create_dir+0x2c/0x70
[ 260.720000] [<c01ed7ba>] kobject_add+0x8a/0x1a0
[ 260.720000] [<c01edac7>] kobject_set_name+0x37/0xb0
[ 260.720000] [<c02557a7>] device_add+0xb7/0x530
[ 260.720000] [<c01ed50f>] kobject_get+0xf/0x20
[ 260.720000] [<c01ed92b>] kobject_init+0x2b/0x40
[ 260.720000] [<eedee60b>] i2c_add_adapter+0x12b/0x280 [i2c_core]
[ 260.720000] [<eede5573>] acpi_ec_hc_add+0x122/0x16b [i2c_ec]
[ 260.720000] [<c02ecd1a>] cond_resched+0x2a/0x40
[ 260.720000] [<c0228a3d>] acpi_bus_driver_init+0x28/0x4b
[ 260.720000] [<c0229ad8>] acpi_bus_register_driver+0x82/0xb7
[ 260.720000] [<eec7e00a>] acpi_ec_hc_init+0xa/0x11 [i2c_ec]
[ 260.720000] [<c014416d>] sys_init_module+0x15d/0x1ba0
[ 260.720000] [<c0107a5d>] sys_mmap2+0xcd/0xd0
[ 260.720000] [<c01031f0>] sysenter_past_esp+0x69/0xa9
[ 260.720000] =======================
[ 260.720000] Code: f6 ff e8 67 d0 f4 ff eb b6 90 8d 74 26 00 83 ec 1c 89 5c 24 0c 89 cb 89 74 24 10 89 c6 89 7c 24 14 89 df 89 6c 24 18 8
9 54 24 08 <8b> 42 0c 83 c0 70 e8 c8 58 13 00 31 c0 b9 ff ff ff ff f2 ae f7
[ 260.720000] EIP: [<c01b7f4d>] create_dir+0x1d/0x1e0 SS:ESP 0068:e007fdc8
[ 260.720000] <3>ibm_acpi: ec object not found
I get a very similar crash (loading ACPI modules dies at kref_get()) on my Mac Pro workstation. 2.6.20-12 did not have this problem. I upgraded all packages at once, so I have the latest ACPI support tools.
I'm back to running 2.6.20-12 with a downgraded nvidia-glx until this gets resolved.