Comment 6 for bug 434376

Switching to AccelMethod "EXA" removes the artifacts, but is terribly slow. I've downgraded to Jaunty's xserver-xorg-video-ati and -radeon drivers, and have no problems with the AccelMethod "XAA" now.

lspci -vvv for the graphics card:
01:00.0 VGA compatible controller: ATI Technologies Inc Radeon Mobility M6 LY
        Subsystem: IBM Device 0235
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping+ SERR+ FastB2B+ DisINTx-
        Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 66 (2000ns min), Cache Line Size: 32 bytes
        Interrupt: pin A routed to IRQ 11
        Region 0: Memory at e0000000 (32-bit, prefetchable) [size=128M]
        Region 1: I/O ports at 3000 [size=256]
        Region 2: Memory at c0100000 (32-bit, non-prefetchable) [size=64K]
        [virtual] Expansion ROM at c0120000 [disabled] [size=128K]
        Capabilities: <access denied>
        Kernel modules: radeon, radeonfb