The kernel seems to be stable on longer testing, I have been using the device whole day with no problems whatsoever. Actually I am now in train writing this on the device itself...
The only feature not working (that I have come across at yet anyway) is the haptic feedback.

I also did some timings of the building process and it is significantly faster than 'traditional' Harmattan kernel build. And the nice thing is that scratchbox is not needed, this builds nicely on normal shell using gnuabi cross-compiler

Building kernel in scratchbox using -j4 takes about 9 minutes alltogether on my fairly dated T9600@2.8GHz. Building the Nemo variant takes only about 7 minutes!

I have not yet made any performance benchmarking on the actual device so all this is subjective, but it feels pretty responsive. I am running with defaults of harmattan, no system tuning or governor tweaks active.