System is very slow, possibly btrfs related

[Alexandre]

The general responsivness of the system is very good, the kwin effect are working perfectly, but for some reason, the last update took 55 minutes to complete (for updating only libreoffice, quassel irc and another small apps), while it should take somehing like 3-4 minutes max I guess.
It "feels" like any file operation 'expanding folders', copying files, are not responsive. For instance, when clicking on the "K" menu from kde, I should wait ~4 seconds for it to show up.

I'm using btrfs for / and for /home, but my /home is encrypted. Perhaps it's related ?
Also, I experienced a kernel panic last session, I couldn't take a picture of it, but it mentionned everywhere "btrfs".
My kernel is tainted though as I installed the ath9k compat-wireless-2011-04-30 driver

$ cat /proc/version_signature
Ubuntu 2.6.38-8.42-generic 2.6.38.2
$ lsb_release -rd
Description: Ubuntu 11.04
Release: 11.04

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: linux-image-2.6.38-8-generic 2.6.38-8.42
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic x86_64
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.23.
Architecture: amd64
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: PCH [HDA Intel PCH], device 0: ALC269VB Analog [ALC269VB Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: acid 1948 F.... pulseaudio
CRDA: Error: [Errno 2] Aucun fichier ou dossier de ce type
Card0.Amixer.info:
 Card hw:0 'PCH'/'HDA Intel PCH at 0xc4820000 irq 48'
   Mixer name : 'Intel CougarPoint HDMI'
   Components : 'HDA:10ec0269,1179062e,00100100 HDA:80862805,11790001,00100000'
   Controls : 25
   Simple ctrls : 11
Date: Tue May 17 14:50:03 2011
EcryptfsInUse: Yes
InstallationMedia: Kubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427)
MachineType: TOSHIBA PORTEGE R830
ProcEnviron:
 LANGUAGE=
 PATH=(custom, user)
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-2.6.38-8-generic root=UUID=2ab582d9-f557-41c6-a00b-7a5801bb9757 ro rootflags=subvol=@ quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-2.6.38-8-generic N/A
 linux-backports-modules-2.6.38-8-generic N/A
 linux-firmware 1.52
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/04/2011
dmi.bios.vendor: TOSHIBA
dmi.bios.version: Version 2.30
dmi.board.asset.tag: 0000000000
dmi.board.name: Portable PC
dmi.board.vendor: TOSHIBA
dmi.board.version: Version A0
dmi.chassis.asset.tag: 0000000000
dmi.chassis.type: 10
dmi.chassis.vendor: TOSHIBA
dmi.chassis.version: Version 1.0
dmi.modalias: dmi:bvnTOSHIBA:bvrVersion2.30:bd04/04/2011:svnTOSHIBA:pnPORTEGER830:pvrPT320E-02D00PFR:rvnTOSHIBA:rnPortablePC:rvrVersionA0:cvnTOSHIBA:ct10:cvrVersion1.0:
dmi.product.name: PORTEGE R830
dmi.product.version: PT320E-02D00PFR
dmi.sys.vendor: TOSHIBA