Excuse the late reply... I am very busy at the moment.
With respect to the thickness: the first attempt on this added about 2-3 mm extra. Though, as it got loose I had to take a second try which now probably adds about 4-5 mm (?). Note that this only adds partially to the advertised overall thickness of the N900 as this includes afaik the bump of the camera slider and stand.
Still, this makes the device look even more clunky. But if you happen to like a diy-ish "MacGyver look" you probably wouldn't mind.

Also note that I experience problems with respect to the USB data connection. I didn't notice this earlier as I do not use this pretty often. I don't know if the problems are related to the optocoupler solution or if any USB related parts in the device got damaged. Unfortunately I am currently lacking the time to investigate this further. Charging via USB still works btw. IIRC the USB data connection did work with the first "dip-switch" solution.

Last but not least, if you like messing with your precious device in a similar way, be sure to check out the pretty informative post by joerg_rw at the bottom of the page: http://talk.maemo.org/showthread.php?t=71414&page=2

Edit:
One last note: I do not charge the device unattended, so I can quickly respond in case something goes wrong. Luckily so far I did not encounter such a circumstance.