JeffLuszcz I am quite interested in this application. I have been wanting to build it since I got my n810 (about 3 months ago). I am interested in a little bit more however. I would like to try and fully emulate an accelerometer with the cam.

There is a company that specializes in this (among other things) called gesturetek. see : http://www.gesturetekmobile.com/ Its a Canadian company and I only found out about it because I spoke to their CTO a few months ago about their multi-touch division.

I am a multi-touch researcher in general so I am no stranger to processing video as input, but I am a bit new to the maemo platform.
If you want to work together and set up a project on maemo garage I would be happy to work on this with you.

I have also read up on a guy who was trying to port openCV to maemo, but was mostly successful. ( I think)
see : http://www.nabble.com/Problem-using-...html#a16326280
and
http://andrew.daviel.org/n810-blog.html
But I think that openCV might be a bit to much bloat for this project anyway.