Even if your N900 die after another year or within next 2 weeks, there is no way of finding out if that was due to overclocking or not. No one will be able to tell really. A bad cpu sample can easily burn out over time even when running at stock speeds. Maybe even after overclocking the N900 to 1.1GHz constant, maybe your GPU might die for no apparent reason. Or maybe just a bad capacitor will blow which had nothing to do with it. Yes, there is a higher probability of failure when running it at higher speed than stock. How much? No one has a clue. There are just way too many variables to consider. =P

BTW, I've damaged 1 item in my life so far while overclocking I think. It was my old ATI Radeon video card. (can't even remember the model now) It was around 8 years ago and after overclocking (both GPU and memory) for a few months, it started to artifact and was persistent even on lower clocks for both GPU and RAM. Not sure if it was the bad RAM or the bad GPU and couldn't find out if overclocking had anything to do with it. It was under warranty so it got replaced. My replacement overclocked even better and never had any issues for nearly 2 years before I upgraded. =P