It is an interesting read - It's a beginners guide to writing code on the Cell. However, it contains no real surprises and definitely no exploits as such.
It's also concentrating on SPE vulnerabilities. Exploiting this is difficult, since the hypervisor (running on a SPE) protects main memory used by both the SPE and PPE. The hypervisor is essentially self-contained after boot - If it has been properly designed (and the lack of a hack after this amount of time suggests nothing else) it has only well defined external interfaces that can't be exploited by any obvious method.
So, to get an exploit in OtherOS or GameOS, you need to cause the hypervisor SPE to run your own code. There are also symptoms which would tend to indicate that there is a "watchdog" to ensure that the hypervisor is still active - If I was implementing this, it would be an external device to the processor that accepts some sort of signed message at 5 second or so intervals which resets the CPU in case of a missed heartbeat.