Personally, I'm convinced that at least -half- the complaints and issues are probably due to a failing/poor sample chip(or other bit of hardware) that works right enough of the time to keep things running - Just like what happens when you OC the device with slightly too little voltage(most things will work, but odd crashes will happen).
Remember also that -technically- the N900's factory OC'd at 600mhz(or at least I heard that somewhere).

The problem is, the OS won't crash most of the time(It's Linux. It's resilient), and as such the users think it's a software problem.
This is why you can have two users, both with the -exact same- software, and one will have constant problems while the other won't.

For example, I've got a good sample, and while I've got it OC'd to 950mhz, I have had -zero- crashes in the last month or so. It's rock-stable, works great, and I have no problems with it. But, that was only -after- I tweaked the voltage; with a "stock" profile it would be unstable at a lot lower than that!