Do not let apmd and acpid run at the same time unless you REALLY know what you're doing. Debian will not make sure only one is running at a time. You will have to check. APM will try to put your system into S3. On the 2.4.x (and before) series kernels this will quite probably hang your machine. S3 is not supported until at least 2.5.x. Even the patch won't provide support for S3 in the 2.4.x series kernels. I personally did an apt-get remove apmd to solve the hanging problem.
You should also be aware of another little glitch I discovered. The XFree86 server has an option for DPMS (Energy Star) features. The DPMS can states can be one of standby, suspend, off or on. Since the 2.4.x kernels cannot suspend to disk, this can cause problems. I fixed my system by doing two things:
xset -dpms (disables DPMS features)
In /etc/X11/XF86Config-4 I commented out the line Option "DPMS" under Section "Monitor".
|Lost Touchpad and Keyboard Interrupts|
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.