Karl Hegbloom emailed me to say that "keyboard keys sticking, touchpad pointer jumping suddenly across the screen, lockups under heavy network I/O [was] caused by polling the battery state via ACPI and the proc file system." This problem caused, in part, by a delay between the initial request for information about the battery's status and the response. In that delay interrupts may be locked out and synchronization with the keyboard and touch pad may be lost. "The overnight solution is to either turn off the battery applet, or reduce its polling frequency." Karl also notes that a BIOS update was also able to solve the problem. Thanks Karl!

I did not find this to be a problem for me in the 2.4.x kernels, however, it was a problem when I upgraded to 2.6.5. I use wmacpi to monitor my battery status. By setting the polling frequency to 1 (the lowest possible number), I seem to have eliminated the touchpad lockups. In my .xinitrc file I use:

/usr/bin/wmacpi -s 1

The -s 1 represents the polling frequency (sample rate) of "once per minute." The default is 20.