I have updated both the hardware setup of my camera remote as well as the software that is used to control the Arduino.
With regard to the hardware, I have soldered the optoisolator and capacitors to a small board. I also bought a remote cable for the Nikon D200 and connected it to my optoisolator, so that the setup can now be connected more easily to the camera.
Here is a description of the circuit:
With regard to the software, I updated my app with further modes for interval shooting and bulb (apart of the existing self timer mode). The new version of the app depends on Android 4.0 (ICS) in order to work properly, as I used the advanced number pickers that are not available in the older versions of Android.
I also pushed all the code to a Bitbucket repository with a small description of how to get this setup to work: https://bitbucket.org/boden/btcamremote/
A description of the initial setup can be found here: https://postapocalypticresearchinstitute.wordpress.com/2012/01/15/bluetooth-camera-remote/