Yep. I operate the device left-handed (hold it in my right and use my left forefinger on the screen) and I have two issues: the screen brightness changes all the time because of the shadow from my finger / hand, and my right hand seems to absorb a lot of the cell signal (the cell antennas are on the right of the device).

The second one only becomes a real issue indoors or in poor coverage areas.

I guess the N900 was meant for right-handed people.