While i did not obtain my N9 through Handtec i found my device affected
as well. I did install PR1.1 today and found it a substantial improvement.

Unfortunately i still get hangs and spontaneous reboots, though less
frequently. Where before i could get the N9 to crash within a few minutes
(typically in the maps application but also the "desktop") it has improved
noticeably.
I no longer see kernel Oops that caused reboots as well as the frequent
crashes of the SGX graphics kernel. So these were at least to some
extent software related.

However i still have seen crashing applications, a hang of the graphics
subsystem and a few reboots. Also my dmesg output still shows ECC
errors. I would tend to assume the ECC errors may well indicate a HW
problem.