When playing TF2 on the latest AMD 12.11 beta 11 drivers,
and with a newer Graphics card, HD68xx to HD79xx
I have the HD7850 graphics card
You will sometimes see a major performance drop compared to the older drivers, and see this being spammed in the developer console:

IDirect3DQuery9::GetData(): Occlusion query flush took 32.843ms!

The current work around is to revert the optimizations that were done in the latest driver patch

sudo sed -i s/hl2/hl3/ /etc/ati/atiogl.xml

But this is still an existing bug.

System Information:

Processor Information:
    Vendor:  GenuineIntel
    Speed: 2667 Mhz
    4 logical processors
    4 physical processors
    HyperThreading:  Unsupported
    FCMOV:  Supported
    SSE2:  Supported
    SSE3:  Supported
    SSSE3:  Supported
    SSE4a:  Unsupported
    SSE41:  Supported
    SSE42:  Supported

Network Information:
    Network Speed:  

Operating System Version:
    Ubuntu 12.04.1 LTS (64 bit)
    Kernel Name:  Linux
    Kernel Version:  3.2.0-23-generic
    X Server vendor:  The X.Org Foundation
    X Server release:  11103000

Video Card:
    Driver:  ATI Technologies Inc. AMD Radeon HD 7800 Series
    Driver Version:  4.2.11995 Compatibility Profile Context
    Desktop Color Depth: 24 bits per pixel
    Monitor Refresh Rate: 60 Hz
    VendorID:  0x1002
    DeviceID:  0x6819
    Number of Monitors:  2
    Number of Logical Video Cards:  1
    Primary Display Resolution:  1920 x 1080
    Desktop Resolution: 3840 x 1080
    Primary Display Size: 18.78" x 10.55"  (21.54" diag)
                                            47.7cm x 26.8cm  (54.7cm diag)
    Primary VRAM Not Detected

Sound card:
    Audio device: VIA VT1828S

Memory:
    RAM:  7976 Mb

Miscellaneous:
    UI Language:  English
    LANG:  en_US.UTF-8
    Microphone:  Not set
    Total Hard Disk Space Available:  790330 Mb
    Largest Free Hard Disk Block:  359563 Mb

Installed software:

Recent Failure Reports:
    Thu Dec 20 07:59:58 2012 GMT: file ''/tmp/dumps/crash_20121220025955_1.dmp'', upload >yes: ''CrashID=bp-4c2abd7e-270-4003-83d9-9ff872121219''