Hi

Thanks for the answers.

I've taken the advice of tomaszrybak and installed the Crash Reporter. I already uploaded some crash reports too.

Mostly these reboots seem to be the consequence of a crashing app (Although I absolutely don't see why the whole system needs to be rebooted because of one crashing app).
In cases (which happen pretty often) when the n900 cancels the boot process and restarts again, no crash report is created (most likely because the needed daemon was not yet running at that time).

@Kechit
Did you have no problem with replacing the phone? Because I think its not that easy to prove that the device has a malfunction, because its hard to demonstrate something which apparently only happens randomly. How did you describe the problem that they believed you?

Thanks in advance!