I have the late-2009 model of the iMac (with the latest version of Lion) and I use a rEFIt CD frequently to switch from OS X to Ubuntu and vice versa. Ubuntu 12.04 is installed on a partition of an external hard drive and the rest is used as a Time Machine.

I've noticed recently that at times, Ubuntu will suddenly freeze everything on the desktop except for the mouse. When this happens, I can unplug the external hard drive and nothing happens; the mouse (Bluetooth) continues to function, but clicking or hovering over anything makes it useless. At this point, I have to manually hold down the Mac's power button and reboot to the rEFIt CD. I've installed the graphics driver it needs and at this point, I can't see what could cause it to freeze like this. Should I just file a bug, or does anyone have any workaround suggestions to unresponsiveness? Thanks in advance.

EDIT it appears that after installing 'nvidia-current,' I have not experienced freezing issues. I'll update this post if it freezes again.