I must give full credit to Ubuntu for an excellent job.
All of the kernel bugs I found, and described above, were in late beta kernels, but by the time of the official release just two weeks later, they all seem to be fixed. That's very good considering how many tricky ones there were. Even the subtle ftrace bug was implicated and fixed in the time window :-)
I took the plunge and am now happily using Intrepid with an Intrepid kernel. :-)