UPDATE Feb 9th, 2012:

A new version is up, magnusplus_0.0.2-1_armel.deb.

Changes:
- A new app added to the package in addition to the magnifier, magnus plus negative viewer, very handy for the ones who use colour and b/w photographic film negatives. It works like magnus plus magnifier, just that it inverts the video stream on the fly.
- Icons for both apps.
- Close focusing fixed, it works now on my both n900s, one powered by power kernel and the other one closer to the stock configuration.

And a hint on how to best use the two applications from the package:
as I didn't find yet a way to disable the opening of the default camera when the camera slide is open, and it actually helps to open that once to fix the exposure and white balance (these settings remain somewhere and are inherited by magnus plus),

Preparation (only once, repeat just when the type and intensity of the light changes):
step1: open the camera slide. The default camera app either starts by itself, or if you have your phone differently configured, you start it.
step 2: half-press the shooting button (don't need to take a photo).
step 3; close the default camera app

Actual use:
With the camera slider already open, just start Magnus plus magnifier or magnus plus negative viewer, find the optimum distance to the object you are interested in and enjoy the magnified (and optionally inverted) view.
Test first non-inverted (the plain magnifier) on your computer display, you should be able to nicely see the pixels.

I appreciate any feedback.