i started working on an acpi driver this evening to make my thinkpad x61 work better under openbsd. i just finished it and so far it matches on the IBM0068 acpi hid device, checks it for the appropriate version, enables the bluetooth device (which is required before the hardware toggle switch can power it on and let the ubt0 device show up), and sets up a callback to run whenever a special button (e.g., fn+f[1-9], brightness, thinklight, etc.) is pressed. i'm pretty sure it will work on most other thinkpads but i haven't tried it on my x40 yet.
i mapped out all of the events that get generated, which on my x61 tablet include the screen rotating around, the lid opening and closing, and even the pen being ejected from its little slot. when the brightness buttons (fn+home and fn+end) are pressed, it sends a cmos command through acpi to actually adjust the screen brightness accordingly, so now it's working just like my x40 did on its own. being able to turn the brightness down when on battery is the main reason i wrote this.