I'm finally confident about the following:
I got 2 Raspberry Pi's of the first generation. One I purchased from Rs Components and one from Element14.
I have made a script that logs in the Pi with Putty and edits a file on /boot and one on /etc (it just adds a comment each time) and then sends a reboot command.
When running the script while the Pi from Rs Components is booted it fails every now and then (corruption of the filesystem). It fails well before 30 tries. At that moment the Pi only had a mouse and keyboard in its USB ports.
Now when running the script while the Pi from Farnell is booted it has run for 224 ! times without failure and then I aborted the script.
I'm using exact the same Power adapter and SDcard (identical contents).
It looks like Pi from RS is faulty but it will be hard to prove this to Rs Components
I suspect everyone in this thread is having a faulty Pi. Maybe it has to do with the brand of memory. My Pi of Rs Components has Hynix memory while the Element14 one has Samsung memory.
The bad news is that Quake III crashes on the Element14 Pi while working fine on the Rs Components Pi so neither of my Pi's is 100% fault free
EDIT: I forgot to say that neither of my Pi's is overclocked