After switching from ati-drivers to x11-drivers/xf86-video-ati-6.12.1-r1 my GPU temperature grow up to 90C and more when I start an OpenGL Application. Without OpenGL the temperature swap around 75C.
My Card is an:
01:00.0 VGA compatible controller: ATI Technologies Inc M10 NT [FireGL Mobility T2] (rev 80)
My Notebook is a IBM R50p
Steps to Reproduce:
1. Follow http://www.gentoo.org/proj/en/desktop/x/x11/ati-migration-guide.xml
2. Xorg --configure
3. copy xorg.conf.new to /etc/X11/xorg.conf
4. Start KDE 3.5
5. Start glxgears
Temperature grow up constant 2 Degrees per minute since 75C.After starting glxgears the temperatur is growing 5 Degrees per minute. My fan turn at 5300 RPM.
cat /proc/acpi/ibm/thermal shows "temperatures: 43 53 39 91 35 -128 32 -128"
A temperature around 50C like the atidrivers fglrx driver.
This is not a packaging issue, ie something we (Gentoo) can fix.
Please file a bug upstream  and paste the url here so we can track the issue.