A few points on graphics glitches experienced in Yosemite on this system with the GeForce 9800GT:
even though Bronya's 10.10 RC2.1 sorts out corruption of desktop icons, it causes very buggy behaviour of Safari and it does not support Duran Keeleys's fixes for AppStore issue (no contents display in app). Same goes with RC3. As such, it's better to revert to Bronya RC1 and apply Duran's AppStore + LaunchPad fixes Edit 11Mar2015: Obsolete now
use attached patched IOGraphicsFamily kext to avoid final boot screen graphics corruption
In all cases, rebuild cache before reboot: sudo chmod -R 755 /S/L/E sudo chown -R 0:0 /S/L/E sudo touch /S/L/E sudo kextcache -Boot -U / Bronya_10.10_RC1.zip IOGraphicsFamily.kext.zip