Wow! Now I understand why I've lost my SD card! Thanks, fellows! But I also lost my camera start-up function when I open the slide on the back cover...are they related too??

Yes, without the magnet the N900 thinks the cover is missing, and hence also the camera door isn't there, so it ignores the signals coming from the sensor that detects whether door is open or closed.

Well, it doesn't exactly ignore these signals, but doesn't start the camera app. Just try the following:

- Remove the back cover.
- Lock the screen (black screen)
- Hold some piece of white paper to the camera's optical door sensor while watching the display display go on.
- Remove the piece of white paper while watching the display switching off.

Fun stuff to play with and see the optical door sensor work! Have fun!