A beef up camera client along the lines of the jail broken canon ones would be a killer app on the N900.
I don't think there are any projects out there to remake the camera app? Probably requires a mini team and quite a lot of time.
__________________
Nokia are a business and have chosen a path of using the OSS community phenomenon to reduce their overheads specifically after sales support and development. Unlike Apple who do the opposite and make a killing from their Applications store.
If the camera app is closed source is it not possible to make a new app for the camera with more features?
Craig