I've also started the beginnings of a radeon performance profile-setting GUI as a way to teach myself GTK. I'll be poking around at this one in my spare time over the next few weeks, and hopefully by the end I'll have something to show for it. Currently targeting only radeons (r100+), but if I can find the right sysfs nodes for Nouveau/Intel/others (PTS can probably show me the way here), there's no reason I couldn't handle them all.
Current features targeted: Change CPU/memory clocks/profiles, report temperatures/frequencies. Eventually, maybe add support for setting fan profiles/speeds when applicable. I'll leave DPMS to KDE/Gnome/etc. X.org feature settings (2D tiling, etc) will probably be left out for now, but might be added in the future.
Please make the user interface portable to other tool kits. I will happily try my coding skills with QT, once I learn enough C++ .